Estimation and Rounding — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
When rounding 47 to the nearest 10 in Grade 4, the answer is 40.
Corrected: When rounding 47 to the nearest 10 in Grade 4, the answer is 50.
The ones digit in 47 is 7, which is 5 or more, so 47 rounds up to 50, not down to 40.
2. Fix the sentence:
In Grade 4, rounding 23 to the nearest 10 gives 30.
Corrected: In Grade 4, rounding 23 to the nearest 10 gives 20.
The ones digit in 23 is 3, which is less than 5, so 23 rounds down to 20, not up to 30.
3. Fix the sentence:
Grade 4 students round 65 to the nearest 10 and get 60.
Corrected: Grade 4 students round 65 to the nearest 10 and get 70.
The 5-or-more rule means a ones digit of 5 rounds up, so 65 rounds to 70, not 60.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Grade 4 rounding: 38 rounded to the nearest 10 is 40.
Because 8 is 5 or more, 38 rounds up to the next ten, which is 40.
2. In Grade 4, 72 rounded to the nearest 10 is 70.
Because 2 is less than 5, 72 rounds down to 70.
3. Grade 4 work: 95 rounded to the nearest 10 equals 100.
Using the 5-or-more rule, 95 rounds up to 100.
4. A Grade 4 student rounds 14 to the nearest 10 and writes 10.
Since 4 is less than 5, 14 rounds down to 10.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain in your own words how a Grade 4 student rounds 56 to the nearest 10.
Sample answer: I look at the ones digit, which is 6. Because 6 is 5 or more, I round up. So 56 rounds to 60.
The ones digit decides the direction. Six is 5 or more, so 56 rounds up to the nearest higher ten, 60.
2. In Grade 4, why does 42 round down to 40 when rounding to the nearest 10?
Sample answer: The ones digit is 2. Because 2 is less than 5, I round down, so 42 becomes 40.
Any ones digit less than 5 keeps the tens place the same, so 42 rounds down to 40.