Estimation Strategies — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
To round 487 to the nearest 100, I get 400.
Corrected: To round 487 to the nearest 100, I get 500.
The tens digit 8 is greater than 5, so 487 rounds up to 500, not down.
2. Fix the sentence:
Front-end estimate of 24 + 38 is 2 + 3 = 5.
Corrected: Front-end estimate of 24 + 38 is 20 + 30 = 50.
Front-end estimation uses 20 and 30 as the leading values, giving a sum near 50.
3. Fix the sentence:
Rounded to the nearest 10, 76 becomes 70.
Corrected: Rounded to the nearest 10, 76 becomes 80.
Because the ones digit 6 is 5 or greater, 76 rounds up to 80, not down to 70.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Rounded to the nearest 10, 47 is 50.
Seven rounds up, turning 47 into 50 at the nearest ten.
2. Rounded to the nearest 100, 312 is 300.
Because the tens digit 1 is below 5, 312 rounds down to 300.
3. The front-end estimate of 58 + 23 is 70.
Front-end keeps 50 and 20, so the estimate sums to 70 quickly.
4. Rounded to the nearest whole number, 6.7 is 7.
Seven tenths is greater than five tenths, so 6.7 rounds up to 7.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Estimate 24 + 38 by rounding each addend to the nearest 10.
Sample answer: 20 + 40 = 60
Rounding 24 to 20 and 38 to 40 gives a quick estimated sum of 60.
2. Estimate $4.85 to the nearest dollar for a quick total.
Sample answer: $5
Because eight tenths is at least five, $4.85 rounds up to $5.