Estimation (Intro) — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A class has 28 red crayons and 33 blue crayons. About how many crayons in all?
A) About 60
B) About 40
C) About 90
D) About 100
28 rounds to 30 and 33 rounds to 30, so 30 + 30 = 60 is the best estimate.
2. Maya read 47 pages Monday and 52 pages Tuesday. Her total was 99. Is that reasonable?
A) Yes, estimate is about 100
B) No, estimate is about 50
C) No, estimate is about 150
D) No, estimate is about 200
47 rounds to 50 and 52 rounds to 50, so 50 + 50 = 100 is close to 99, making 99 reasonable.
3. A farm has 61 hens and 18 ducks. Which estimate of the total birds is best?
A) About 80
B) About 50
C) About 100
D) About 40
61 rounds to 60 and 18 rounds to 20, so 60 + 20 = 80 is the best estimate.
4. Leo had 82 stickers and gave away 39. He said he has 43 left. Is that reasonable?
A) Yes, estimate is about 40
B) No, estimate is about 60
C) No, estimate is about 20
D) No, estimate is about 80
80 - 40 = 40, which is close to 43, so Leo's answer is reasonable.
Part B: Fill in the Blank
Write the correct answer on each line.
1. If 28 + 33 rounds to 30 + 30, the estimate is 60.
30 + 30 = 60, and this matches the actual sum 61 closely.
2. Rounded estimate of 47 + 52 is 50 + 50 = 100.
50 + 50 = 100 is very close to the exact 99, so 99 is reasonable.
3. Rounded estimate of 61 + 18 is 60 + 20 = 80.
60 + 20 = 80, and the actual 79 is just 1 away so it makes sense.
4. Rounded estimate of 82 - 39 is 80 - 40 = 40.
80 - 40 = 40 matches closely with the actual 43, so Leo's answer is reasonable.
5. Estimation helps you quickly check if an answer is reasonable.
Estimates give a quick benchmark to judge whether the exact answer makes sense in a story problem.