simple interest.50
TRANSCRIPT
Simple Interest
1. What is the SI onRs.2500/- at the rate of 12% per annum for 8 years? Ans :2400
Difficulty Level : Easy Yes Moderately easy Difficult
Basic Formula:
Simple Interest is denoted by SI
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Answer with Explanation:
Given P = 2500, N = 8 Years, R = 12%
There fore S.I =
S.I =
S.I = 2400
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2. What is the SI on Rs.7500/- at the rate of 10% per annum for 5 years? Ans 3750
Difficulty Level : Easy Yes Moderately easy Difficult
Basic Formula:
Simple Interest is denoted by SI
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Answer with Explanation:
Given P = 7500, N = 5 Years, R = 10%
There fore S.I =
S.I =
= 75 X 5 X 10
S.I = 3750
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3. A man borrowed rs.5000/- at the rate of 8% SI and to clear the debt after 6 years, how much he has to return : Ans 7400
Difficulty Level : Easy Moderately easy Yes Difficult
Basic Formula:
Simple Interest is denoted by SI
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Answer with Explanation:
Given P = 5000, N = 6 Years, R = 8%
There fore S.I = PNR / 100
S.I =
= 50 X 6 X 8
S.I = 2400
Total repayment = S.I + Principal amount
Answer = 2400 + 5000 = Rs 7400
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4. A man borrowed Rs.8000 at the rate of 12% SI, and lent the same sum to another person at the rate of 15% what will be the gain after 7 year ? ans 1680
Difficulty Level : Easy Moderately easy Difficult Yes
Basic Formula:
Answer with Explanation:Given :
A man borrowed at 12%
He lent the same sume to another person at 15%
Therefore his gain is 15 – 12 =3% for 1 year
Given N = 7 years and P = Rs. 8000
First we are calculating for Rs. 100
For 100 = 3 X 7 = 21
For 1000 = 210
For 8000 = 1680
Therefore his gain = Rs. 1680/-
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5. Mr.A borrowed Rs.12000/- at the rate of 10% and lent the same amount to Mr.B. at the rate of 13% what will be gain of A, after 5 years. Ans 1800
Difficulty Level : Easy Moderately easy Yes Difficult
Basic Formula:
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Answer with Explanation:
Given P = 12000, N = 5 years,
(i) R = 10%, (ii) R = 13%
Case (i)
S.I =
=
= Rs. 6000/-
Case (ii):
S.I =
=
= Rs. 7800/-
Difference = Rs. 7800 – Rs. 6000
= Rs. 1800/-
Therefore Gain = Rs. 1800/-
Note : Problems 4 and 5 both are same type. So either you follow the method given in 4th problem (or) 5th problem.
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6. In what time, we can get Rs.1200/- as SI on Rs.5000/- at the rate of 8%? Ans 3
Difficulty Level : Easy Moderately easy Yes Difficult
Basic Formula:
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Time = Number of years (N)
Answer with Explanation:
Given :
S.I. = Rs. 1200/-
P = Rs. 5000/-
R = 8%
To find time (Number of years (N) )
1200 =
1200 = 400 N
N = 1200/400
N = 3
Therefore N = 3 years
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7. In what time RS.6000/- give RS.2880/-as SI at the rate of 12%? Ans 4
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
P – Principal amount, N- Number of years, R – Rate of Interest
Time = Number of years (N)
Answer with Explanation:
Given :
S.I. = Rs. 2800/-
P = Rs. 6000/-
R = 12%
To find time (Number of years (N) )
2800 =
2800 = 720 N
N = 2800/720
N = 4
Therefore N = 4 years
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8. Mr. Manager took a loan of Rs.25000/- for 5years at SI. If the interest paid were Rs.12500/- what is the rate of interest per annum? Ans10%
Difficulty Level : Easy Yes Moderately easy Difficult
Basic Formula:
S.I =
Interest = Simple Interest
Answer with Explanation:
Given :
P = Rs. 25000/-
S.I = Rs. 12500/-
N = 5 Years
To find R
12500 =
R = 12500 / 1250
= 10%
Therefore the Rate of Interest = 10%
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9. Mr. Thiru borrowed Rs.50000/- for 3 years at SI. If the interest paid was Rs.18000/- find the rate of SI? Ans 12%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Interest = Simple Interest
Answer with Explanation:Given :
P = Rs. 50000/-
S.I = Rs. 18000/-
N = 3 Years
To find R
12500 =
R = 18000 / 1500
= 180 / 15
= 12
Therefore the Rate of Interest = 12 %
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10. Mr.Raj got a loan at 11% p.a. SI after 5 years he returned the principal along with interest. If he returns in all RS.12400/- what is the principal amount Ans:8000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given R = 11%, N = 5 years, S.I + P = Rs.12400/-
To find P,
We know that S.I =
S.I + P = + P
(ie) 12400 = + P
12400 = +P
12400 = P { +1}
= P { }
P = 12400 X 100/155
P = Rs. 8000/-
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11. Mr.Krishnan received a loan at 13% p.a. SI. After 4 years he returned the principal and interest. If he returned Rs.9120/- what will be principal amount ? Ans:6000
Difficulty Level : Easy Yes Moderately easy Difficult
Basic Formula:
Note : Problems 10 and 11 are of same type. So you can follow either the following method or 10th problem method.
Answer with Explanation:
Given
R = 13%, N = 4 years, S.I + P = Rs.9120/-
Short cut method:
First we are calculating for Rs. 100/-
100 = 13 X 4 (R X N) for number of years
100 = 152 (Amount =100 and the Interest = 52)
? = 9120
P = 100 X 9120 / 152
P = 6000
Principal Amount = Rs.6000/-
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12. If Rs.700/- amount to Rs.16800/- in 5 years SI. If the rate of interest is increased by 5%. It would amount to how much? Answer : Rs.10,150
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
Given rate of interest is increased, so we add the given amount and the calculated amount
Answer with Explanation:
P = Rs. 700, N= 5 years, Increased rate of interest R = 5%
Short cut method:
First we are calculating it for 100 rupees
100 : 5 X 5 = 25 (NXR)
700 : 25 X 7 = 175
Given amount + S,I = Rs. 16800 + 175 = 16975
Therefore the amount = Rs. 16975/-
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13. If Rs.12000/- amount to Rs.16800/- in 5 years If the rate of interest is increased by 2%. What would be the amount? Answer : Rs.18,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
Given rate of interest is increased, so we add the given amount and the calculated amount
Answer with Explanation:P = Rs. 12000, N= 5 years, Increased rate of interest R = 2%
Short cut method:
First we are calculating it for 100 rupees
100 : 5 X 2 = 10 (NXR)
(ie) for 100 rupees the interest is Rs. 10100 = 101000 = 10010000 = 10002000 = 200
There for 12000 = 1000 + 200 = 1200Given amount + S,I = Rs. 16800 + 1200 = 18000
Therefore the amount = Rs. 18000/-
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14. If Rs.10,000/- amount to Rs.14000/- in 5 years If the rate of interest is reduced by 3%. What would be amount? Answer : Rs.12,500
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
Given rate of interest is reduced, so we subtract the given amount and the calculated amount
Answer with Explanation:P = Rs. 10000, N= 5 years, Increased rate of interest R = 3%
Short cut method:
First we are calculating it for 100 rupees
100 : 5 X 3 = 15 (NXR)
(ie) for 100 rupees the interest is Rs. 15100 = 151000 = 15010000 = 1500
Given amount + S,I = Rs. 14000 - 1500 = 12500
Therefore the amount = Rs. 12500/-
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15. A principal amount to RS.8880/- in 4 years and Rs.9600/- in 5 years what is the rate of interest?Ans 12%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Amount = Principal + S.I
Answer with Explanation:
S,I for one Year = Rs.720 (9600 – 8880)
S.I for 4 years = Rs.2880
Principal = Amount – S.I
= 8880 – 2880
= 6000
R =
=
= 288/6X 4
= 48/4 = 12
Therefore R = 12%.
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16. A certain sum of money lent out of SI amount to Rs.8000/- 6 years Rs.9000/- in 8 Years. Find the sum and the rate of interest? Answer 10%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Amount = Principal + S.I
Answer with Explanation:Given:
S.I for 2 years = 1000 (9000-8000)
(8-6)
S.I. for 1 year = 500
S.I for 6 years = 3000
P = Amount – S.I
= 8000-3000
P = 5000
R =
= 100/10
R = 10%
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17. A certain sum give RS.9000/- as SI for 8 years at the rate of 12% what will be the
SI on the same sum for 12 years at the rate of 8% ?
Answer: 9000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
We split the given problem into 2 parts
Part (i)
Given S.I = 9000, N = 8, R = 12
S.I. =
9000 = ------------------(1)
Part (ii)
Given N=2, R = 8
S.I. = ------------------(2)
From (1) and (2), S.I = Rs. 9000/-
Shortcut method:
Number of years in Part (i) = Rate of interest in Part (ii)
Rate of interest is part (i) = Number of years in part (ii)
S.I. = Rs. 9000/-
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18.A Principal amount give Rs.12000/- as SI for 7 years at the rate of 11% to get the same amount of interest of 11 years, what will be the rate of interest
Ans.: 7%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Results:
Number of years in Part (i) = Rate of interest in Part (ii)
Rate of interest is part (i) = Number of years in part (ii)
Answer with Explanation:
We split the given problem into 2 parts
Part (i)
Given P = 12000, N = 7, R = 11
Part (ii)
Given P = 12000, N = 11,
Using the results(in the formula),
R = 7%
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19.Mr.A. give Rs.1500/- to Mr.X for 4 years and Rs.2500/- to mr.Y. for 8 years. If the rate of intest is the same and Mr.A received Rs.2080/- from both Mr.X and mr.Y what is the rate of SI ?
ans: 8%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given :
For X, P = 1500, N = A
For Y, P = 2500, N= 8
S.I = Rs. 2080 ( For X and Y)
+ = 2080
60R + 200R = 2080
260R = 2080
R = 2080 / 260
R = 8%
Rate of interest of SI = 8%
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20.Ms.Varshini gave Rs.30000/- to Mr.Suresh for 5 years and Rs.20000/- to Mr.Vijay for 2 ½ years. If the rate of interests is the same and she received Rs.14000//- as SI from both. What is the rate of interest?
Ans: 7%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given :
X : Ms.Varshini, Y: Mr.Vijay
For X, P = Rs.30000/-, N=5
For Y, P= Rs.20000/-, N= 2 ½
S.I = Rs. 14,000 (For X and Y)
+ = 14000
1500R +500R = 14000
2000 R = 14000
2R = 14
R = 7
Rate of interest = 7%
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21.What would be the SI on Rs.48000/- for 4 years at the rate of 6 ¼% :Ans 12,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:Given:
P = Rs. 48000/-, N = 4, R = 6 ¼
S.I =
=
= 480 X 25
= 12000
S.I = 12,000
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22 What will be the SI on Rs.60000/- for 3 years at the rate of 8 1/3% Ans 15,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given,
P = Rs. 60,000, N=3, R = 8 1/3
S.I =
S.I =
=
= 600 X 25 = 15,000
S.I = Rs. 15,000/-
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23 What will be the SI on Rs.75000/- for 3 years at the rate of 16 2/3% Ans 37,500
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given,
P = Rs. 75,000, N=3, R = 16 2/3
S.I =
S.I =
=
= 750 X 50 = 37500
S.I = Rs. 37500/-
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24 What will be the SI on Rs.25000/- for 3 years at the rate of 33 1/3% Ans 25,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:
Given,
P = Rs.25,000, N=3, R = 33 1/3
S.I =
S.I =
=
= = 25,000
S.I = Rs. 25,000/-
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25 A sum of money becomes double in 10 years. What is the rate of interests Ans:10%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation:Given : N = 10
Let the sum be x, Then S.I = x
Given a sum becomes double
S.I = Sum
S.I = becomes
X =
100x = 10x X R
X = 10
Rate of Interest = 10%
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26. A person borrows Rs. 5000 for 2 years at 4% p.a. simple interest. He
immediately lends it to another person at 6 1/4% p.a. for 2 years. Find his gain in
the transaction per year.
Rs.112.50 Rs.125 Rs.150 Rs.167.50
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
We split the given problem into 2 parts
Part (i)
Given P = Rs. 5000, N=2, R = 4%
S.I = = 100X 4
S.I = 400
Part (ii)
Given P = Rs. 5000, N=2, R = 6 ¼ %
S.I = = = = 25 X 25
S.I = 625
Gain = 625 -400 = 225 for 2 years
Gain for one year = Rs. 112.50
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27. How much time will it take for an amount of Rs.450 to yield Rs.81 as interest at 4.5% p.a. of simple interest?
3.5 years 4 years 4.5 years 5 years
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Time = Number of years
Answer with Explanation
Given P = Rs. 450, S.I=Rs. 81/-, R = 4.5%
S.I = becomes
81 =
81 = 2025N / 100
8100 = 2025N
N = 8100 / 2025
N = 4
Number of Years = 4
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28. What is the present worth of Rs.132 due to 2 years at 5% simple interest per
annum?
Rs.112 Rs.118.80 Rs.120 Rs.20,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
Let the present worth be x ( ie Principal = x)
Then S.I = Rs (132 – x)
Given N = 2, R = 5
S.I = becomes
132-x =
132-x = 10x / 100
132-x = x/10 1320 – 10x = x
11x = 1320
X = 1320 / 11 = 120
Present worth = Rs. 120/-
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29. In how many years, Rs.150 will produce the same interest at 8% as Rs.800
produce in 3 years at 4 1/2%?
6 8 9 12
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation We split the given problem into 2 parts
Part (i)
Given P = 150, R = 8
S.I. = ------------------(1)
Part (ii)
Given P = Rs. 800/- N=3, R = 4 ½
S.I. = =
= ------------------(2)
From (1) and (2),
= = 4 X 3 X9
3 X N X 4 = 4 X 3 X 9
N = 9
Number of Years = 9
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30. Nitin borrowed some money at the rate of 6% p.a. for the first three years, 9% p.a. for the next five years and 13% p.a. for the period beyond eight years. If the total interest paid by him at the end of eleven years is Rs.8160, how much money did he borrow?
Rs.8000 Rs.10, 000 Rs.12, 000 Rs.1500
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
We split the given problem into 3 parts
Part (i) R = 6, N = 3
Part (ii) R = 9, N=3
Part (iii) R = 13, N = 11-8 = 3
S.I = Rs. 8160/-
+ + = 8160
+ + = 8160
= 8160 = 8160
102 P = 816000
P = = 8000
P = Rs. 8000/-
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31. What will be the difference between simple and compound interest at 10% per
annum on a sum of Rs.1000 after 4 years?
Rs.31 Rs.64.10 Rs.40.40 Rs.40.45 Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
C.I = P N
Answer with Explanation
(i) S.I =
S.I = 100 X4
S.I = 400
(ii) C.I = 1000 4 - 1000
=1000 4 – 1000 = 1000 4 - 1000
=1000 X X X X - 1000
=1464.1 – 1000 = 464.1
C.I. = 464.1
Difference = C.I – S.I = 464.1 – 400 = 64.10
Difference = 64.10
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32. A sum of money at simple interest amounts to Rs.815 in 3 years and to Rs.854
in 4 years. The sum is:
Rs.650 Rs.690 Rs.698 Rs.700
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
Answer with Explanation Given:
Amount at SI for 3 years = Rs. 815
Amount at SI for 4 years = Rs. 854
SI for 1 year = (854 – 815 = Rs. 39/-
SI for 3 years = 39 X 3 = 117
Amount = Rs (815-117) = 698
Amount = Rs. 698/-
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33. A sum of money trebles itself in 15 years 6 months. In how many years would it double itself?
6 years 3 months 7 years 9 months 8 years 3 months 9 years 6 months
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Amount = Sum + S.I
Answer with Explanation
Let sum = x, Then SI = 2x
S.I = becomes [ Sum + SI = x +2x = 3x]
2x = [ N = 15 ½ = 31/2]
200 = 31/2 RR = 400/31
Now sum = x, S.I =x [ Sum + SI = 2x = Double the amount]
X =
100x =
31 = 4N N = 31/4 7 ¾
N = 7 years 9 months
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34. In how much time would the simple interest on a certain sum be 0.125 times
the principal at 10% per annum?
1 1/4 years 1 3/4 years 2 1/4 years 2 3/4 years
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
R =
Answer with Explanation
Let Principal = x
Given simple interest = .125 time the principal
(ie) SI = .125x
= x = 125x/1000
S.I = 1/8x
Given R = 10%
S.I = becomes
1 x /8 = 1 x /8 = Nx/10
1/8 = N/10 N = 10/8 = 5/4 years
N = 1 ¼ years
Time = 1 ¼ years
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35. Simple interest on a certain amount is 9/16 of the principal. If the numbers
representing the rate of interest in percent and time in years he equal, then time, for
which the principal is lent out, is:
5 1/2 years 6 1/2 years 7 years 7 1/2 years
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
Given Simple interest = 9/16 of the principal
(ie) S.I = P ----------------------(1)
Given Rate of interest = Time in Years
(ie) R = N ------------------(2)
= S.I becomes
= P [from (1) and (2)]
= N2 =
N = = 7.5
N = 7 ½ Years
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36. The difference between compound interest and simple interest on an amount of Rs.15, 000 for 2 years is Rs.96. What is the rate of interest per annum?
8 10 12 None of these
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
C.I = P N – P
(a+ b)2 = a2 + 2ab + b2
Answer with Explanation
Given P = Rs.15000, N = 2
C.I – S.I = Rs. 96/-
- = 96
- = 96
15000 - 15000 X = 96
15000 = 96
15000 = 96
= 96 R2 = R2 = 64 , R = 8
Rate of Interest = 8%
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37. A lent Rs.5000 to B for 2 years and Rs.3000 to C for 4 years on simple interest
at the same rate of interest and received Rs.2200 in all from both of them as
interest. The rate of interest per annum is:
5% 7% 8% 10%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation We split the given problem into 2 parts
Given
Part (i) P=Rs.5000, N = 2
Part (ii) P = Rs. 3000/-, N = 4
S.I = Rs. 2200/-
2200 = +
2200 = 100R +120R
2200 = 220R
R = 2200/220
R = 10
Rate of Interest = 10%
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38. What will be the ratio of simple interest earned by certain amount at the same rate of interest for 6 years and that for 9 Years?Answer : 2:3
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
Answer with Explanation Let P = Principal, R- Rate of interest
Case (i)
N = 6
Case (ii)
N = 9
Ratio = = 6PR / 9PR
6/9 = 2: 3
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39. At what rate per cent per annum will be simple interest on a sum of money be 2/5 of the amount in 10 years?Answer : 4%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
R =
Answer with Explanation
Given
N = 10
Let Sum = x (Principal amount)
S.I = 2x / 5
R = becomes
R =
R = 2 X 2 = 4
R = 4
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40. A man borrowed certain amount for 6 years at the rate of 5% and paid a SI of Rs. 1230. What is the principal amount? Answer : Rs. 4100
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
Given
N = 6, R = 5, S.I = 1230
S.I = becomes
1230 =
1230 = 6P/20 3P/10
3P = 12300
P = 4100
Amount = Rs. 4100/-
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41. Rs. 2,500 earns simple interest of Rs. 1750 after 7 years. Had the interest been 2% more, how much more interest would it have earned?Answer : 350
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
Given
P = Rs. 2500/-, N = 7, R = 2,
S.I = becomes
=
= 25 X 7 X 2 = 350
More interest is Rs. 350/-
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42. A sum of money becomes 5/4 of itself in 5 years at a certain rate of interest. What is the rate of interest?Answer : 5%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I = Sum = Principal
R = Amount = Principal +SI
Answer with Explanation
Let sum = x
Then Amount = 5x/4
S.I = Amount – Sum
= 5x/4 –x = 1x/4
R =
R = 25/5
R = 5%
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43. At what rate percent per annum will a sum of money double in 16 years ?Answer : 6.25%
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Amount = Principal +SI
Answer with Explanation
Given
Let Sum = x
Then SI =x, time = 16 years { ( SI + Sum = double the amount) x+x = 2x}
x =
= R
R = 100/16 = 50/8 = 25/4
R = 12.5/2
R = 6.25%
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44. The simple interest on a sum of money is 4/9 of the principal. Find the rate percent and time, if both are numerically equal.Answer: 6 Years 8 Months
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation
Given
(i) S.I = 4P/5
(ii) Rate percent = Time
(ie ) R = N
S.I = becomes
P =
=
9N2 = 400
N2 = 400/9 20/3 = N
N = 6 years 2/3 years
N = 6 years 8 months
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45. A man took loan from a bank at the rate of 12% p.a. simple interest. After 3 years he had to pay Rs.5400 interest only. The principal amount borrowed by him was:Answer : 15,000
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Answer with Explanation Given
S.I = Rs. 5400/-, N = 3, r=12
S.I = becomes
5400 =
5400 =
18P = 270000
P = = 15,000
Principal amount = Rs. 15,000/-
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46. If the sum of money double in 5 years. It will become 4 times in ?Answer : 15
Difficulty Level : Easy Moderately easy Difficult
Basic Formula:
S.I =
Amount = Principal +SI
Answer with Explanation
Given
Let Sum = x, Then SI =x,
S.I = becomes
x =
R = R = 20% ( SI + Sum = 3x +x = 4x)
Now, Sum = x, S.I = 3x, R = 20%
S.I = becomes
3x = 3 =
2N = 30 N = 15
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