Estimating Decimals Sums and Differences

Estimating Decimals

​What does estimate mean?

​Estimate- to roughly calculate a number or value.

​

​An estimation is not exact. When you estimate, you use the knowledge and information you have to make an educated guess about a number.

​

​Estimating is usually a quicker way to get an answer than calculating.

Multiple Choice

True or false:

An estimation is an exact answer.

• True

• False

​When is it okay to estimate?

​It is okay to estimate when a problem uses words such as roughly, approximately, or about.

​

Example:

​Approximately how many gumballs are in the jar?

​

​Instead of counting each gumball, you would

estimate how many gumballs are in the jar by

​looking and thinking about what would be a

​reasonable answer.

​

​There are about 70 gumballs in the jar.

Multiple Choice

Which symbol means approximately equal to?

• $$=$$  

• $$\ne$$  

• ?

• $$\approx$$  

​When we estimate decimals, we must remember what we've learned about rounding decimals.

​

Multiple Choice

What is 5.8 rounded to the nearest whole number?

(Remember "whole number" means ones place)

• 5

• 6

• 4

• 7

Multiple Choice

What is 38.3 rounded to the nearest whole number?

• 38

• 39

• 30

• 40

Multiple Choice

What is 56.4 rounded to the nearest TENS place?

(Remember to find the place and look next door.)

• 57

• 50

• 60

• 56

​When you're estimating a sum or difference:

• ​Round the numbers first

• ​Then add or subtract

Estimate the sum.

Multiple Choice

Estimate the sum.

16.9 + 8.3 ≈ __

• 25

• 26

• 24

• 20

Multiple Choice

Estimate the difference.

38.2 - 4.8 ≈ __

• 30

• 32

• 33

• 34

​You can also use compatible numbers to estimate.

Multiple Choice

Estimate the difference.

802.74  -  478.95  ≈  ___

• 800

• 300

• 400

• 500