Estimating with Whole Numbers

Definitions:

Compatible Numbers – Are numbers that are close to the actual numbers in a math problem.

Estimate - Is an answer that is close to the exact answer and is found by rounding.

Underestimate – An estimate that is less than the exact answer.

Overestimate - A estimate that is greater than the exact answer.

Estimating a Sum of Difference by RoundingEstimate the sum or difference by rounding to the indicated place value.Example 1:5,439 + 7,516; thousands

5,439 5,000+ 7,516 + 8,000

13,000The sum of 5,439 and 7,516 is approximately 13,000.

Example 2:62,167 – 47,511; ten-thousands

62,167 60,000- 47,511 - 50,000

10,000The difference of 62,167 and 47,511 is approximately 10,000.

Strategy:1.) Round each number to the indicated place value.2.) Apply the indicated operation.

Estimating a Sum of Difference by RoundingEstimate the sum or difference by rounding to the greatest place value.Example 3:611 + 378

611 600+ 378 + 400

1,000The sum of 611 and 378 is approximately 1,000.

Example 4:45,709 – 11,250

45,709 50,000- 11,250 - 10,000

40,000The difference of 45,709 and 11,250 is approximately 40,000.

Strategy:1.) Round each number to the largest place value.2.) Apply the indicated operation.

Try these: Estimate the sum or difference by rounding to the indicated place value.

1.) 11,245 + 12, 768, ten thousands 2.) 581 – 354, hundreds

Try these: Estimate the sum or difference by rounding to the greatest place value.

3.) 110,490 + 252,881 4.) 6,611 – 4,449

Estimating a Sum of Difference by Rounding

Estimating with Whole Numbers

Let’s try these:

1.) Ms. Escobar is planning a graduation celebration for the entire 8th grade. There are 9 eight-grade homeroom classes of 27 students. Estimate how many cups Ms. Escobar needs to buy for the students if they all attend the celebration.

2.) Mrs. Byrd will drive 120 miles to take Becca to the state fair. She can drive 65 miles per hour. About how long will the trip take?