2nd grade · Math · Unit 17 of 17
About How Many?
Round, estimate and check
What your child practices
Rounding to the nearest ten or hundred to estimate sums and differences, and using an estimate to check whether an answer makes sense. Estimation is a California addition to the 2nd grade standards.
California Content Standards learning standard: 2.NBT.7.1 · using estimation strategies to make reasonable estimates in problem solving
How we explain it
Children can open this short lesson before they practice.
- To estimate, round each number to a friendly number, like the nearest ten or hundred.
- Add or subtract the rounded numbers in your head.
- Use the estimate to check: a real answer should be close to it.
Example: About how much is 38 + 41? Round to the nearest ten. 38 is about 40. 41 is about 40. 40 + 40 = 80. Answer: about 80
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Round each number to the nearest hundred. About how much is 955 − 547?
- 200
- 500
- 300
- 700
500
Hint: 955 is about 1000 and 547 is about 500. 1000 − 500 = 500.
Question 2
Round each number to the nearest hundred. About how much is 408 + 412?
- 800
- 500
- 1000
- 900
800
Hint: 408 is about 400 and 412 is about 400. 400 + 400 = 800.
Question 3
Leo adds 161 + 420. Which answer is reasonable?
- 581
- 181
- 981
- 1381
581
Hint: Estimate first: about 600. The reasonable answer is close to 600.
Question 4
A bakery makes 18 muffins and 44 bagels. About how many baked treats is that? Round to the nearest ten.
- 90
- 40
- 70
- 60
60
Hint: 18 is about 20. 44 is about 40. 20 + 40 = 60.
Question 5
What is 56 rounded to the nearest ten?
- 60
- 70
- 30
- 40
60
Hint: Look at the ones digit. 56 is closer to 60.
Question 6
Round each number to the nearest hundred. About how much is 838 − 343?
- 700
- 500
- 400
- 200
500
Hint: 838 is about 800 and 343 is about 300. 800 − 300 = 500.