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 2.367 to the nearest tenth: 2.3 because we drop the rest.
Corrected: Round 2.367 to the nearest tenth: 2.4 because the hundredths digit is 6.
When the digit after the rounding place is 5 or greater, the rounding digit increases by one.
2. Fix the sentence:
Round $4.78 to the nearest dollar: $4 because we keep the whole part.
Corrected: Round $4.78 to the nearest dollar: $5 because $.78 is closer to one dollar.
Seventy-eight cents passes the halfway point, so the dollar amount rounds up by one.
3. Fix the sentence:
Estimate $3.49 plus $2.51 by rounding to $3 and $2 to get $5.
Corrected: Estimate $3.49 plus $2.51 by rounding to $3 and $3 to get $6.
$2.51 rounds up to $3 because fifty-one cents passes the halfway mark cleanly.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Round 5.482 to the nearest tenth to get 5.5.
The hundredths digit 8 is greater than 5, so the tenths digit rounds up.
2. Round 7.234 to the nearest hundredth to get 7.23.
The thousandths digit 4 is less than 5, so the hundredths digit stays the same.
3. Estimate $6.89 plus $2.10 by rounding to whole dollars to get $9.
$6.89 rounds to $7 and $2.10 rounds to $2, giving a total estimate of $9.
4. If a snack costs $3.78 and you pay with $5, estimated change is about $1.
$3.78 rounds to $4, and $5 minus $4 leaves about $1 in estimated change.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain how to round 9.456 to the nearest hundredth in Grade 5.
Sample answer: Look at the thousandths digit, which is 6. Because 6 is 5 or greater, round the hundredths digit up from 5 to 6, giving 9.46.
The digit after the rounding place decides whether the hundredths digit increases or stays the same.
2. Why is rounding to the nearest dollar useful when estimating a grocery total?
Sample answer: Rounding to whole dollars makes mental math fast and gives a close total. Shoppers can quickly check if they have enough money before reaching the register.
Whole-dollar rounding simplifies addition and gives a quick, reliable total estimate.