Estimation Strategies — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Round 0.847 to the nearest tenth: 0.7 because we cut off the extras.
Corrected: Round 0.847 to the nearest tenth: 0.8 because the hundredths digit is 4.
The hundredths digit 4 is less than 5, so the tenths digit stays the same at 8.
2. Fix the sentence:
Estimate $1.99 plus $4.05 as $1 plus $4, totaling $5.
Corrected: Estimate $1.99 plus $4.05 as $2 plus $4, totaling $6.
$1.99 is one cent away from $2, so it rounds up, not down to $1.
3. Fix the sentence:
Round 12.345 to the nearest hundredth: 12.34 by ignoring the last digit.
Corrected: Round 12.345 to the nearest hundredth: 12.35 because the thousandths digit is 5.
A digit of 5 in the next place rounds the hundredths digit up by standard rules.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Round 3.629 to the nearest tenth to get 3.6.
The hundredths digit 2 is less than 5, so the tenths digit stays at 6.
2. Round 8.475 to the nearest hundredth to get 8.48.
Because the thousandths digit is 5, the hundredths digit increases from 7 to 8.
3. Estimate $9.85 plus $4.10 by rounding to whole dollars to get $14.
$9.85 rounds to $10 and $4.10 rounds to $4, giving a quick total of $14.
4. If a book costs $7.20 and you pay with $10, estimated change is about $3.
$7.20 rounds to $7, and $10 minus $7 leaves about $3 in change.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. How would a Grade 5 student round 4.572 to the nearest tenth, and why?
Sample answer: Look at the hundredths digit, which is 7. Since 7 is greater than 5, the tenths digit rounds up from 5 to 6, giving 4.6.
Digits 5 or higher push the rounding digit up by one to the next number.
2. Describe how to estimate the total of three items priced $2.95, $1.80, and $4.10.
Sample answer: Round each price to the nearest dollar to get $3, $2, and $4. Add the rounded amounts to get an estimated total of about $9.
Rounding before adding gives a fast, close estimate without exact decimal addition.