Rounding to Check Your Answer
Maths: Year 5 & 6 National Curriculum, topic 1.2.4
Using Rounding to the Nearest 1,000 to Check Your Answers
You can use rounding to check if our answers are correct. You can use rounding to check your answers from written methods or mental maths.
Example
- I have worked out that 3,427 + 2,372 = 6,699 but I'm not very confident in my answer.
- I can use rounding to check if my answer is roughly correct.
Round both numbers
- I can round both numbers to the nearest 10/100/1,000 to check.
- 3,427 to the nearest thousand is 3,000.
- 2,372 to the nearest thousand is 2,000.
Adding the rounded numbers
- I can add the rounded numbers together to make an estimate for the actual answer.
- 3,000 + 2,000 = 5,000
- As I am rounding to the nearest 1,000, my ‘real’ answer needs to be up to 1,000 away from my estimate if it is correct.
Is it less than 1,000 away?
- I originally said that 3,427 + 2,372 = 6,699.
- 6,699 is more than 1,000 away from our estimated answer (5,000).
- This means that 6,699 is NOT the correct answer and I should try again.
Using Rounding to the Nearest 100 to Check Your Answers
You can use rounding to check if our answers are correct. You can use rounding to check your answers from written methods or mental maths.
Example
- My friend tried to work out the answer to 3,427 + 2,372 to help me.
- My friend thinks 3,427 + 2,372 = 5,799.
- We need to use rounding to check the answer.
Round both numbers
- To get a more accurate estimate, I will round to the nearest 100 this time to work out my estimate.
- 3,427 to the nearest hundred is 3,400.
- 2,372 to the nearest hundred it would be 2,400.
Adding the rounded numbers
- I can add the rounded numbers together to make an estimate for the actual answer.
- 3,400 + 2,400 = 5,800
- As I am rounding to the nearest 100, my friend's ‘real’ answer needs to be up to 100 away from my estimate if it is correct.
Is it less than 100 away?
- My friend originally said that 3,427 + 2,372 = 5,799.
- 5,799 is less than 100 away from our estimated answer (5,800).
- This means that 5,799 could be the correct answer.
- This doesn't mean it is definitely correct though.
Test yourself on Rounding to Check Your Answer
Which of these would be a reasonable estimate for 2,947 + 6,284?
Which of these would be a reasonable estimate for 3,832 + 1,295?
Which of these would be a reasonable estimate for 1,145 + 2,814?
Which of these calculations will give the most accurate estimate for 3,872 + 7,230?
Which of these calculations will give the most accurate estimate for 1,512 + 3,327?