Estimation (Intro) — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. Estimate of 48 + 32 is 80. Exact is 80. This is reasonable.
An exact answer equal to the estimate is very close, so it is reasonable.
2. Estimate of 29 + 41 is 70. Exact is 70, so the exact is equal the estimate.
70 equals 70, so the exact answer matches the estimate exactly.
3. Estimate of 63 - 18 is 40. Exact is 45. The exact is close to the estimate.
A gap of only 5 means the exact answer is close to the estimate, so the work is reasonable.
4. Estimate of 52 + 37 is 90. Exact is 89. Difference from estimate is 1.
90 - 89 = 1, showing the estimate is only 1 off from the exact answer.
5. If an estimate is 60 but the exact is 130, the exact is far from the estimate.
A gap of 70 is large, so the exact answer is far from the estimate and something may be wrong.
6. Close estimates help us catch mistakes in our math.
If the exact is far from the estimate, it likely signals a calculation mistake to fix.
7. Estimate of 71 - 29 is 40. Exact 42 is near the estimate.
A 2-unit gap means the answer is near the estimate, so 42 looks reasonable.
8. When the exact answer is very far from the estimate, we should check our work.
A big gap between estimate and exact is a signal to check work for errors.
9. An estimate close to the exact means the exact is reasonable.
When estimate and exact are close, the exact answer is reasonable and probably correct.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Est 80, exact 80
→ Exact matches estimate
Exact matches estimate
Est 40, exact 45
→ Close, off by 5
Close, off by 5
Est 90, exact 89
→ Very close, off by 1
Very close, off by 1
Est 60, exact 130
→ Far, check work
Far, check work
Matching scenarios to their reasonableness shows when an answer looks right and when to recheck.