park forest math team
TRANSCRIPT
Park Forest Math Team
Meet #33
Self-study Packet
Problem Categories for this Meet (in addition to topics of earlier meets):
1. Mystery: Problem solving 2. Geometry: Properties of Polygons, Pythagorean Theorem 3. Number Theory: Bases, Scientific Notation 4. Arithmetic: Integral Powers (positive, negative, and zero), roots up to the sixth 5. Algebra: Absolute Value, Inequalities in one variable including interpreting line graphs
Important information you need to know regarding ALGEBRA Absolute value; inequalities in one variable including interpreting line graphs
Absolute Value is the distance a number is from zero. Absolute value is never negative. The symbol for absolute value is
and
Inequalities
• To solve an inequality, solve as if it were a regular equation. Remember to switch the direction of the inequality sign only if you multiply or divide by a negative!
Category 5 Algebra Meet #3, January 2001 1. Find the positive difference between the two values of x that make the following equation true.
2 7 19x − =
2. Find the set of all the integer values of x, such that
10 3x
>
3. The solution set of the equation ( )9 3 6 10x x C+ − − < is given by the graph shown below. What value of C will make this true?
Answers 1. _______________ 2. { }x =
3. _______________
-6 0 6 x
Solutions to Category 5 Algebra Meet #3, January 2001
Answers 1. 19 2. { }x = − − −3 2 11 2 3, , , , , 3. 44
1. To solve an equation with absolute value we must pursue two possibilities. In this case, 2 7x − could equal 19 or −19 .
2 7 19x − = 2 7 19x − =− 2 26x = 2 12x=− x = 13 x=−6 The positive difference between these two solutions is 19. 2. The absolute value of x must remain small so that the quotient remains greater than 3. The six possibilities are as follows:
x= = >−−3 103
313
3, x= = >−−2 102
5 3,
x= = >−−1 101
10 3, x = = >1 101
10 3,
x = = >2 102
5 3, x = = >3 103
313
3,
The set, then, is { }x = − − −3 2 11 2 3, , , , , . 3. First we distribute and combine like terms.
( )9 3 6 10x x C+ − − < 9 18 3 10x x C+ − − < 6 8x C< −
x C< − 86
We see from the line graph that the solution is
x < 6 . That means that C − =86
6 . Now we
solve for C. C − =8 36, so C = 44 .
Category 5 Algebra Meet #3, January, 2003 1. Given the following set of numbers, find the absolute value of the difference between the sum of the absolute values of the numbers and the absolute value of the sum of the numbers.
-10, 14, - 5, 7, - 3, - 9, 1{ }
2. For how many integer values of n is
28n − 3 a positive integer?
3. For what value of a is the solution set of the inequality below given by the graph below?
3 2x − 7( )+ 9 − 11x < 3a
Answers 1. _______________ 2. _______________ 3. _______________
0 1 2 3 4 5 6 7 8 9 10 11 -1 -2
Solutions to Category 5 Algebra Meet #3, January, 2003
1. First let’s find the sum of the absolute values of the numbers in the set: -10 + 14 + -5 + 7 + −3 + −9 + 1 = 10 + 14 + 5 + 7 + 3 + 9 +1 = 49. Now let’s find the absolute value of the sum of the numbers in the set: -10 +14 + -5 + 7 + -3 + -9 + 1 = −5 = 5. Finally, the absolute value of the difference is 49 − 5 =44.
2. For the expression
28n − 3 to have an integer value, the denominator, n − 3 ,
must be a factor of 28. There are six positive factors of 28 (namely 1, 2, 4, 7, 14, and 28) and the corresponding six negative factors of 28. Thus there are twelve (12) different values of n for which the expression is an integer. It is not necessary to determine those values of n, but they are -25, -11, -4, -1, 1, 2, 4, 5, 7, 10, 17, and 31. 3. The graph shows x > 6. Distributing and combining like terms, we get:
3 2x − 7( )+ 9 − 11x < 3a 6x − 21 + 9 −11x < 3a
−5x − 12 < 3a Adding 12 to both sides we get:
−5x < 3a + 12 When we divide both sides of the equation by -5, the inequality switches direction, so we have:
x > 3a +12−5
Now we must find the value of a so that the expression on the right equals 6. 3a +12
−5= 6
3a +12 = −30
3a = −42 a = −14
Answers 1. 44 2. 12 3. -14
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Category 5 Algebra Meet #3, January 2005 1. Find the positive difference between the two solutions of the equation below.
6x − 4 = 36 2. How many integer values of n make the following inequality a true statement?
5 < 28n
3. For what value of B is the solution set of the equation below given by the graph below? 3 4x + 5( )− 9x + B ≤ 48
Answers 1. _______________ 2. _______________ 3. _______________
0 5 -5
x
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Solutions to Category 5 Average team got 15.88 points, or 1.3 questions correct Algebra Meet #3, January 2005
1. To solve the equation 6x − 4 = 36, we need to solve for both the positive and the negative results.
6x − 4 = 366x = 40
x = 406
6x − 4 = −36
6x = −32
x = −326
The positive difference between these two solutions is
406
− −326
= 406
+ 326
= 726
= 12
2. The inequality 5 < 28n
is true for the following ten
(10) integer values of n: -5, -4, -3, -2, -1, 1, 2, 3, 4, 5.
3. The solution set given by the line graph is x ≤ 5. If we solve the inequality for x, we get:
12x + 15 − 9x + B ≤ 483x + 15 + B ≤ 48
3x ≤ 33 − B
x ≤ 33 − B3
x ≤ 11− B3
We now want to know when 11 – B/3 is equal to 5. We can solve the related equation 11 – 5 = B/3, for which B must be 18.
Answers 1. 12 2. 10 3. 18
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Category 5 Algebra Meet #3, January 2007 1. How many integer values of n make the following statement true?
6n
≥ 1
2. Solve the following inequality. Write your solution with the x on the left, the appropriate inequality sign in the middle, and a mixed number in lowest terms on the right.
−3 6x + 7( )≤ 54 3. Let A be the sum of the absolute values of the numbers in the set below. Let B be the absolute value of the sum of the numbers in the same set. List all possible positive differences between A and B if x is an integer.
{-5, 7, x}
Answers 1. _______________ 2. _______________ 3. _______________
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Solutions to Category 5 Algebra Meet #3, January 2007
1. If n has a value greater than 6 or less than –6, then the
absolute value of the fraction 6n
will be less than one and the
statement will be false. For any value of n between –6 and 6 (including these end points), the statement will be true. There are 6 + 1 + 6 = 13 integers in that range, but we cannot include
zero since 60
is undefined. Therefore, there are just 12 integer
values of n that make the statement true. 2. Let’s divide both sides of the inequality by –3 first, remembering that we must switch the direction of the inequality sign when we divide by a negative.
−3 6x + 7( )≤ 546x + 7 ≥ −18
Next, we subtract 7 from both sides of the inequality, divide by 6, and make a mixed number as follows.
6x ≥ −25
x ≥ −256
x ≥ −4 16
3. If x = 0, then A = −5 + 7 + 0 = 12 and B = −5 + 7 + 0 = 2. The positive difference between A and B is 10. If x = 1, then A = −5 + 7 + 1 = 13 and B = −5 + 7 + 1 = 3, and the difference is still 10. The difference remains 10 for all positive values of x. If x = -1, then A = −5 + 7 + −1 = 13 and B = −5 + 7 + −1 = 1, and the difference is 12. If x = -2, then A = −5 + 7 + −2 = 14 and B = −5 + 7 + −2 = 0, and the difference is 14. If x = -3, then A = −5 + 7 + −3 = 15 and B = −5 + 7 + −3 = 1, and the difference is still 14. For all values of x less than or equal to –2, the difference is 14. The possible differences are 10, 12, 14.
Answers 1. 12
2. x ≥ −4 16
3. 10, 12, 14
Category 5 Algebra Meet #3, January 2009 1. What is the least possible solution for in the inequality below?
2. For what value of does the solution to the inequality below match the
graph below?
3. Mike chose 3 distinct numbers from the set below and took the absolute
value of their sum. Sean chose 3 distinct numbers (not necessarily different from Mike’s) from the set below and took the sum of their absolute values. What is the greatest possible absolute value of the difference between Mike’s and Sean’s result?
60
Answers
1. _______________
2. _______________
3. _______________
Solutions to Category 5 Algebra Meet #3, January 2009
1. So – 4 is the least integer solution for .
2.
Because we’ve divided by if is a negative number, we would have to reverse the to . According to the graph, the solution is which means the inequality was reversed and must be negative. Therefore we
actually have and since we know the equation below finds .
3. To get the largest absolute value of a sum Mike wants to pick numbers that are all positive or all negative so that he is adding their values. The largest he could get would be . The smallest value Mike could get would be or . For Sean to get the largest sum of the absolute values he just needs the three numbers with the largest absolute values. In this case he wants for which the sum of their absolute values is The smallest value he could get would be . The greatest possible difference between Mike’s result and Sean’s result would be by taking Sean’s largest (30) and Mike’s smallest (0).
Answers 1. 2. 3. 30
Meet #3 January 2011
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Category 5 Algebra
1. How many integers satisfy the inequality below?
2. The solution of the inequality is given by: .
What is the value of the parameter ?
3. The solution to the inequality is given by the line graph below.
What is the value of ?
Answers
1. _______________
2. _______________
3. _______________
N+8 N
Meet #3 January 2011
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Solutions to Category 5 - Algebra
1. We can rewrite the inequality as
or . This is true for the integers in the range
- a total of integers.
2. When solving , if the argument inside the absolute value is positive
we get , and if it is negative we get . Comparing this to
the given solution we see that .
3. When solving , if the argument is positive we get
. Comparing these to
the line graph we conclude that .
Answers
1.
2.
3.
Category 5 Algebra Meet #3, January 2013 1. Solve the following inequality. Write your solution with the x on the left, the appropriate inequality sign in the middle, and a mixed number in lowest terms on the right.
€
7 5x +19( )−2>40 2. For his birthday, Jarod received $54 from his Aunt Edna and three gift cards from his Uncle Joe. Although the gift cards are for different stores, each gift card has the same dollar value. If the absolute value of the difference between the money from Aunt Edna and the value of the three gift cards from Uncle Joe is $18, what is the absolute value of the difference between the two possible amounts that each gift card is worth? 3. How many integer values of n make the following inequality true?
€
2<20n
Answers
1. _____________________
2. $ ___________________
3. ____________ integers
Solutions to Category 5 Algebra Meet #3, January 2013
1.
€
7 5x +19( )−2>40
7 5x +19( ) >42
5x +19>65x > −13
x >−135
x > −2 35
or
€
7 5x +19( )−2>40
35x +133−2>4035x +131>40
35x > −915x > −13
x > −2 35
2. We can capture this idea in the absolute value equation
€
54−3x =18, where x is the unknown value of each gift card. To solve this, we consider two separate equations as shown above. The absolute value of the difference between $24 and $12 is $24 – $12 = $12. 3. Since there is an absolute value sign in this inequality, we need to solve two separate inequalities as shown below.
€
2<20n
2n <20n <10
and
€
2> −20n
2n > −20n > −10
We need to find values of n that satisfy both inequalities, so it helps to write the solution as the compound inequality
€
−10< n <10 . The 18 integers in this range are n = -‐9, -‐8, -‐7, -‐6, -‐5, -‐4, -‐3, -‐2, -‐1, 1, 2, 3, 4, 5, 6, 7, 8, and 9. We have to skip n = 0, since we cannot divide by zero.
Answers
1.
€
x > −235
2. $12
3. 18 integers
€
54 −3x =1854 −18 =3x
36 =3xx =12
€
54 −3x = −1854 +18 =3x
72=3xx =24