Estimating a Sum of Whole Numbers

The whole numbers are first rounded as specified, i.e., rounded to the nearest ten, hundred and so on. Then the sum of the rounded whole numbers is found to estimate the sum of the whole numbers.

Estimate the sum 3,273 + 8,781 + 11,309, by first rounding each number to the nearest thousand.

Solution

Step 1:

In 3,273, the hundreds digit, 2 is less than 5. So we round down 3,273 to the nearest thousand 3,000.

Step 2:

In 8,781, the hundreds digit, 7 is greater than 5. So we round up 8,781 to 9,000.

Step 3:

In 11,309, the hundreds digit, 3 is less than 5. So we round down 11,309 to the nearest thousand 11,000.

Step 4:

So the estimated sum is 3,000 + 9,000 + 11,000 = 23,000.

Estimate the sum 514 + 2,327 + 119, by first rounding each number to the nearest hundred.

Solution

Step 1:

In 514, the tens digit, 1 is less than 5. So we round down 514 to the nearest hundred 500.

Step 2:

In 2,327, the tens digit, 2 is less than 5. So we round down 2,327 to nearest hundred 2,300.

Step 3:

In 119, the tens digit, 1 is less than 5. So we round down 119 to the nearest hundred 100.

Step 4:

So the estimated sum is 500 + 2,300 + 100 = 2,900.