Estimation and Rounding — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Is 12,346 a reasonable answer for 5,890 + 3,456?
A) Yes, because the estimate is about 9,300
B) No, because the estimate is about 9,300 and 12,346 is much larger
C) Yes, because both are close
D) No, because the estimate is about 15,000
5,900 + 3,500 = 9,400, so an answer of 12,346 is far from the estimate and is not reasonable.
2. Is 4,210 a reasonable answer for 8,732 - 4,567?
A) No, the estimate is about 9,000
B) Yes, the estimate is about 4,200
C) No, the estimate is about 5,000
D) Yes, the estimate is about 13,000
8,700 - 4,600 = 4,100, which is close to 4,210, so the answer is reasonable.
3. Is 1,800 a reasonable estimate for 32 x 58?
A) Yes, because 30 x 60 = 1,800
B) No, because 30 x 50 = 1,500
C) Yes, because 40 x 50 = 2,000
D) No, because 32 x 58 = 100
Rounding gives 30 x 60 = 1,800, so 1,800 is a reasonable estimate of 32 x 58.
4. A student says 487 divided by 7 is about 700. Is that reasonable?
A) Yes, because 490 divided by 7 is 70
B) No, because 490 divided by 7 is 70, not 700
C) Yes, because 487 is close to 700
D) No, because the answer is exactly 7
490 divided by 7 is 70, so the correct estimate is 70, not 700. The student's answer is not reasonable.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Estimate the sum 4,892 + 3,107 by rounding each addend to the nearest thousand. The estimate is 8,000.
5,000 + 3,000 = 8,000, a reasonable estimate of the actual sum.
2. Estimate 9,431 - 2,876 by rounding each number to the nearest thousand. The estimate is 6,000.
9,000 - 3,000 = 6,000, an approximate value for the difference.
3. If a student answers 6,890 + 2,145 = 9,035, the estimate using thousands is about 9,000.
7,000 + 2,000 = 9,000, which is close to 9,035, so the answer is reasonable.
4. If 47 x 22 has a true product of 1,034, the compatible-number estimate is 1,000.
50 x 20 = 1,000, which is close to the actual product 1,034.
5. If 396 divided by 4 has the answer 99, a reasonable compatible-number estimate is 100.
400 divided by 4 = 100, a clean estimate that is close to the exact answer 99.