Estimation Strategies — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Rounded to the nearest 1000, 4,621 is 4,000.
Corrected: Rounded to the nearest 1000, 4,621 is 5,000.
Because the hundreds digit 6 is at least 5, 4,621 rounds up to 5,000.
2. Fix the sentence:
Front-end estimate of 312 + 489 is 3 + 4 = 7.
Corrected: Front-end estimate of 312 + 489 is 300 + 400 = 700.
Three hundred plus four hundred equals 700, a useful front-end estimate.
3. Fix the sentence:
Rounded to the nearest whole, 8.4 is 9.
Corrected: Rounded to the nearest whole, 8.4 is 8.
Because four tenths is below the halfway mark, 8.4 rounds down to 8.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Rounded to the nearest 100, 850 is 900.
Five tens triggers rounding up, so 850 becomes 900 at the nearest hundred.
2. Rounded to the nearest 1000, 7,238 is 7,000.
Because two hundreds is less than five hundred, 7,238 rounds down to 7,000.
3. Front-end estimate of 612 - 198 is 400.
Six hundred minus two hundred gives an estimate of 400 quickly.
4. Rounded to the nearest 10, $34 is about $30.
Four ones rounds down, so $34 becomes $30 to the nearest ten dollars.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Estimate 487 + 612 by rounding each to the nearest 100.
Sample answer: 500 + 600 = 1,100
Rounding gives 500 plus 600, an estimated total of 1,100 for the sum.
2. Estimate $19.75 + $8.40 to the nearest dollar.
Sample answer: $20 + $8 = $28
$19.75 rounds to $20 and $8.40 rounds to $8, totaling about $28.