Rounding to Nearest 10 and 100 — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. What is 638 rounded to the nearest hundred?
A) 600
B) 630
C) 640
D) 700
To round to the nearest hundred, check the tens digit. In 638 the tens digit is 3, which is less than 5, so 638 rounds down to 600.
2. A class collects 56 cans on Monday and 37 cans on Tuesday. About how many cans total when rounded to the nearest ten?
A) 80
B) 90
C) 100
D) 110
Round 56 up to 60 and 37 up to 40, then add: 60 + 40 = 100. Rounding each number first makes it easy to estimate the total.
3. Which number rounds to 400 when rounded to the nearest hundred?
A) 339
B) 348
C) 351
D) 449
The tens digit in 351 is 5, and when the digit is 5 you round up. So 351 rounds up to 400, making it the correct match.
4. What is the best estimate for 84 - 39 when both numbers are rounded to the nearest ten?
A) 40
B) 50
C) 60
D) 70
Round 84 down to 80 and 39 up to 40, then subtract: 80 - 40 = 40. This gives a quick estimate close to the exact answer of 45.
Part B: Fill in the Blank
Write the correct answer on each line.
1. 482 rounded to the nearest hundred is 500.
The tens digit in 482 is 8, which is 5 or greater, so 482 rounds up to 500.
2. 29 + 53 is about 80 when each number is rounded to the nearest ten.
Round 29 down to 30 and 53 down to 50, then add: 30 + 50 = 80. Estimating with rounded numbers is a fast way to check your work.
3. 673 rounded to the nearest ten is 670.
The ones digit in 673 is 3, which is less than 5, so 673 rounds down to 670.
4. When rounding 750 to the nearest hundred, the answer is 800.
The tens digit in 750 is exactly 5, and the rule says to round up when the digit is 5. So 750 rounds up to 800.
5. 81 - 34 is about 50 when each number is rounded to the nearest ten.
Round 81 down to 80 and 34 down to 30, then subtract: 80 - 30 = 50. This estimate is close to the exact answer of 47.