Use front-end estimation with adjustment to estimate each of the following:
a. 2345 + 5250 + 4210 + 910
b. 345 + 518 + 655 + 270
a. 2300 + 5300 + 4200 + 900 = 12,700.
b. 300 + 500 + 700 + 300 = 1800.
To use front-end estimation with adjustment, follow these steps:
Step 1: Identify the front-end digits
Look at the leading digits of each number. These are the digits on the leftmost side of each number.
Step 2: Add the front-end digits
Add up the front-end digits to get an estimated sum.
Step 3: Adjust the estimate
If any of the other digits in the numbers are 5 or greater, add 1 to the estimated sum. If any of the other digits are less than 5, leave the estimated sum as is.
Let's use this method to estimate the sums:
a. 2345 + 5250 + 4210 + 910
Step 1: The front-end digits are 2 from 2345, 5 from 5250, 4 from 4210, and 9 from 910.
Step 2: The estimated sum of the front-end digits is 2 + 5 + 4 + 9 = 20.
Step 3: Adjust the estimate. Since the other digits are all less than 5, we don't need to adjust the estimate. The estimated sum is 20.
b. 345 + 518 + 655 + 270
Step 1: The front-end digits are 3 from 345, 5 from 518, 6 from 655, and 2 from 270.
Step 2: The estimated sum of the front-end digits is 3 + 5 + 6 + 2 = 16.
Step 3: Adjust the estimate. Since the other digits are all less than 5, we don't need to adjust the estimate. The estimated sum is 16.
Therefore, the estimated sums are:
a. 2345 + 5250 + 4210 + 910 ≈ 20
b. 345 + 518 + 655 + 270 ≈ 16