Estimating and Solving Applied Problems
Using Decimals
 Doing Arithmetic of Decimals Using Estimation
Since arithmetic can be cumbersome when it involves complicated numbers, it
is convenient to know how to estimate to get a ball park figure. A
useful method for estimating is to round each number so that there is only
one nonzero digit.
Example
Estimate 23.487201 + 38.48291
Solution
We round each number and then add
20 +
40 = 60
Example
Estimate 9.376 x 0.035912
Solution
We round each number and then multiply
9 x
0.04
Since
9 x 4 = 36
and there are two total digits to the right of the decimal places, we
get
9 x 0.04 = 0.36
Example
Estimate 0.015 ÷ 3.407
Solution
We round each number and then divide
0.01 ÷
3
Since we are only keeping one nonzero digit, we only keep one nonzero
digit for our estimation.
.0033
3
.0100
9
10
The solution is approximately 0.003
Exercises
Use estimation to approximate the following.
 143.2153 + 255.91829
 56.09812  31.2516
 8.98102 x 3.25175
 0.00354 ÷ 0.04218
 Applications
Example
The total snowfall was 37.3 inches in January,
41.5 inches in February, and
18.7 inches in March. What was the average monthly snowfall during
these three months?
Solution
By definition, to find the average we add up all three numbers and divide by
3.
37.3
41.5
+ 18.7
97.5
Now divide by 3
32.5
3
97.5
9
07
6
15
The average monthly snowfall was 32.5 inches.
Example
You make $8.75 per hour at your job for regular work and time and a half for
work over 40 hours. If you work
48 hours this week, how much will you
earn?
Solution
First find the amount for the first 40 hours. This is a
multiplication problem.
8.75
x 40
0
35000
350.00
Now compute the overtime wages
8.75
x 1.5
4375
8750
13.125
Now find the earnings for 8 hours of overtime by multiplying
13.125
x 8
105.000
Now add the regular wages and the overtime wages
350
+ 105
455
You made $455 for the week.
Back to the Decimals page
Back to the Math 187A
page
Back to the Math
Department page
email
Questions and Suggestions
