4.4 Estimating with Decimals

Homework

Mental Math

Give a whole-number estimate for these decimal addition problems. Show which whole numbers you used:

3.8 + 9.9 = EXAMPLE: 4 + 10 = 14

2.7 + 8.1 = 10.5 – 6.6 =

8.8 + 8.9 = 23.7 – 8.8 =

25.5 + 11.9 = 26.2 – 10.8 =

Math MessageTurn to a tablemate and describe two examples

in which decimals are used in real-life situations.

Measurement:

Money:

Other:

Why are decimals useful?SRB Page 26:

Trip Meters and Speedometers

What information would we get if it just showed whole numbers of miles traveled?

Decimals make it possible to have a more precise measurement of distance traveled. Below the

speedometer shows tenths of a mile.

Have you traveled closer to 45 miles or 46?

How do I round decimals?

• Rounding decimals are very similar to rounding whole numbers-the only difference is there is a decimal point!

• Look at the digit to the right of the place you are rounding

• Think about this poem

If it is 4 or less just ignore,

If it is 5 or more add one more!

Rounding to the nearest tenth• Round to the nearest tenth

5.263– The number to the right of the 2 is a six.– Six is greater than five, so I need to add one more

the 2. The 2 becomes a 3 and everything after becomes a 0

– 5.263 rounded to the nearest tenth become 5.300 or 5.3

Rounding to the Nearest Hundredth

• Round to the nearest hundredth• Remember 4 or less just ignore, 5 or more

add one more!• 3.653 The number to the right of the 5 is

an 3. 3 is less than 4, so we just ignore-meaning the five in the hundredths place stays the same.

• The 5 stays the same and all the other numbers after it become zeros

The correct answer is: 3.650 or 3.65

More Practice

• 2.34

• 46.675

• 232.23

• 96.782

• 0.45

• 12.322

Estimating Decimal Sums MJ p 85

Must answer the questions by using ESTIMATION, not by calculating exact

answers.

Partnership Work – MJ p. 83

MJ 85

Wrapping it UP!

• In your math notebook, solve the following problems using estimation.

3.67 + 0.7

5.23 - 1.1

Write one new fact you learned about estimating decimals.

Homework – Study Link 4.4

Math Box 4.4