Lesson 3-5
Example 1 Estimate with Large Numbers
Estimate the total number of sandwiches sold weekly at Burger World if 32.562 thousand burgers are sold and 18.344 thousand chicken sandwiches are sold.
Round each number to the nearest ten for easier adding.
32.562 → 30 32.562 rounds to 30.
+ 18.344 → + 20 18.344 rounds to 20.
50
About 50 thousand sandwiches are sold per week.
Example 2 Estimate with Large Numbers
Chicken Express sells 38.982 thousand chicken sandwiches each week. Estimate how many more chicken sandwiches are sold each week by Chicken Express than Burger World.
38.982 → 40 38.982 rounds to 40.
− 18.344 → − 20 18.344 rounds to 20.
20
About 20 thousand more chicken sandwiches are sold by Chicken Express.
Example 3 Estimate with Small Numbers
Estimate 1.973 + 2.006 + 1.799 using clustering.
The addends are clustered around 2. Round each decimal to 2.
1.973 → 2
2.006 → 2
+ 1.799 → + 2
6
Using clustering, 1.973 + 2.006 + 1.799 is about 6.
Example 4 Real-World Example
Year / Snowfall (in.)2002 / 19.53
2003 / 20.61
2004 / 18.95
2005 / 20.42
The table shows the number of inches of snow in a city for each year. Use clustering to determine the total amount of snowfall for the four years?
The addends are clustered around 20. Round each decimal to 20.
19.53 → 20
20.61 → 20
18.95 → 20
20.44 → 20
Multiplication is repeated addition. So, a good estimate of the total inches of snowfall for the four years is 4 ´ 20, or 80.
Example 5 Use Front-End Estimation
Estimate 42.5 + 31.3 using front-end estimation.
42.5 → 40.0 Add the leftmost digits.
+ 31.3 → + 30.0
70.0
Using front-end estimation, 42.5 + 31.3 is about 70.0.