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Add Decimals and Estimate Answers

In this worksheet, students will be asked to round decimal numbers to the nearest whole number and then estimate the answer to an addition.

'Add Decimals and Estimate Answers' worksheet

Key stage:  KS 2

Curriculum topic:   Number: Addition, Subtraction, Multiplication and Division

Curriculum subtopic:   Use Estimation to Check Answers

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

In this worksheet, you will be asked to round decimal numbers to the nearest whole number and then estimate the answer to an addition.

 

Recap of rounding:

 

What is 35 rounded to the nearest 10?

If the 'one' of the number is less than 5, the number needs to be rounded down.

If the 'one' of the number is 5 or above, the number needs to be rounded up.

So 35 would be rounded up to 40.

 

What is 834 rounded to the nearest 100?

834 would be rounded down to 800 because the tens digit is less than 50 so the number is rounded down.

 

What is 3.9 rounded to the nearest whole number?

Answer: 4

Look at the number after the decimal point, 9. As 9 is greater than 5, you round the 3 to the left of it, up to 4. 

 

Example:

Estimate the answer to the addition by first rounding the decimal numbers.

10.2 + 1.4 = 10 + 1 = 11

 

Now it's your turn!

 

Estimate the answer by rounding the numbers to the nearest 10.

 

63 + 29  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 63 to the nearest 10 and B would be 29 to the nearest 10.

Column A

Column B

B
60
C
30
A
90

Estimate the answer by rounding the numbers to the nearest 100.

 

199 + 141  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 199 to the nearest 100 and B would be 141 to the nearest 100.

Column A

Column B

C
300
A
100
B
200

Estimate the answer by rounding the decimal numbers to the nearest whole number.

 

17.4 + 8.6  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 17.4 to the nearest whole number and B would be 8.6 to the nearest whole number.

Column A

Column B

C
17
A
9
B
26

Can you choose the correct calculation for 12.9 + 4.2 when the numbers are rounded to the nearest whole number?

13 + 6 = 19

13 + 4 = 17

12 + 4 = 16

12.5 + 4.0 = 16.5

Can you choose the correct calculation for 33.3 + 12.8 when the numbers are rounded to the nearest whole number?

33 + 12 = 35

32 + 13 = 45

33 + 13 = 46

33.3 + 13 = 46.3

Estimate the answer to addition below by rounding both numbers to the nearest whole number. 

 

54.9 + 11.1 A + B = C

 

Remember to choose your answers so that they match the sequence.

 661155
A
B
C

Estimate the answer to the addition by first rounding both numbers to the nearest whole number. 

 

46.1 + 21.7 A + B = C

 

Remember to choose your answers so that they match the sequence.

 224668
A
B
C

71.0 + 26.9 = ?

 

Can you fill in the blank spaces below by rounding the decimal numbers to the nearest whole number?

 224668
A
B
C

86.6 + 10.8 = ?

 

Can you fill in the blank spaces below by rounding the decimal numbers to the nearest whole number?

 224668
A
B
C

Estimate the answer to the addition by rounding both decimal numbers to the nearest whole number.

 

55.6 + 32.1 = ? 

56 + 32 = 88

55 + 32 = 87

57 + 33 = 88

5.6 + 3.2 = 8.8

  • Question 1

Estimate the answer by rounding the numbers to the nearest 10.

 

63 + 29  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 63 to the nearest 10 and B would be 29 to the nearest 10.

CORRECT ANSWER

Column A

Column B

B
30
C
90
A
60
EDDIE SAYS
How did you find rounding to the nearest 10? 63 is rounded down to 60 29 is rounded up to 30 60 + 30 = 90
  • Question 2

Estimate the answer by rounding the numbers to the nearest 100.

 

199 + 141  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 199 to the nearest 100 and B would be 141 to the nearest 100.

CORRECT ANSWER

Column A

Column B

C
300
A
200
B
100
EDDIE SAYS
Were you able to round to the nearest 100? 199 is rounded up to 200 141 is rounded down to 100 200 + 100 = 300 Are you beginning to feel more confident? Great focus, let's keep practising!
  • Question 3

Estimate the answer by rounding the decimal numbers to the nearest whole number.

 

17.4 + 8.6  A + B = C

 

Put your answers in the same sequence as the question.

For example, A would be 17.4 to the nearest whole number and B would be 8.6 to the nearest whole number.

CORRECT ANSWER

Column A

Column B

C
26
A
17
B
9
EDDIE SAYS
Decimal numbers can seem tricky but we simply follow the same rules for rounding. Remember to look at the first number after the decimal point. 17.4 is rounded down to 17 8.6 is rounded up to 9 17 + 9 = 26
  • Question 4

Can you choose the correct calculation for 12.9 + 4.2 when the numbers are rounded to the nearest whole number?

CORRECT ANSWER
13 + 4 = 17
EDDIE SAYS
This question required that you look carefully in order to spot the correct calculation which is; 13 + 4 = 17 Why? Because in your working, 12.9 would round up to 13 and 4.2 would round down to 4.
  • Question 5

Can you choose the correct calculation for 33.3 + 12.8 when the numbers are rounded to the nearest whole number?

CORRECT ANSWER
33 + 13 = 46
EDDIE SAYS
For this question, we round 33.3 down and 12.8 up, which leaves us with; 33 + 13 = 46 You're getting stronger at this with each question! You're halfway, keep going.
  • Question 6

Estimate the answer to addition below by rounding both numbers to the nearest whole number. 

 

54.9 + 11.1 A + B = C

 

Remember to choose your answers so that they match the sequence.

CORRECT ANSWER
 661155
A
B
C
EDDIE SAYS
When rounding 54.9 + 11.1, we round 54.9 up to 55 and 11.1 down to 11. This gives us the final sum; 55 + 11 = 66
  • Question 7

Estimate the answer to the addition by first rounding both numbers to the nearest whole number. 

 

46.1 + 21.7 A + B = C

 

Remember to choose your answers so that they match the sequence.

CORRECT ANSWER
 224668
A
B
C
EDDIE SAYS
When rounding 46.1 + 21.7, we round 46.1 down to 46 and 21.7 up to 22. This gives us the calculation; 46 + 22 = 68 Remember to always look at the number after the decimal point and then follow our usual rounding rules. You've got this.
  • Question 8

71.0 + 26.9 = ?

 

Can you fill in the blank spaces below by rounding the decimal numbers to the nearest whole number?

CORRECT ANSWER
EDDIE SAYS
This question had a little challenge in it as 71 didn't need to be rounded, it's already a whole integer. The correct calculation after rounding is; 71 + 27 = 98
  • Question 9

86.6 + 10.8 = ?

 

Can you fill in the blank spaces below by rounding the decimal numbers to the nearest whole number?

CORRECT ANSWER
EDDIE SAYS
How did you find filling in the blank spaces? The correct calculation after rounding is; 87 + 11 = 98
  • Question 10

Estimate the answer to the addition by rounding both decimal numbers to the nearest whole number.

 

55.6 + 32.1 = ? 

CORRECT ANSWER
56 + 32 = 88
EDDIE SAYS
I'm sure you are getting the hang of this rounding now! So, 55.6 rounds up to 56 and 32.1 rounds down to 32. 56 + 32 = 88 That’s another activity ticked off!
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