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Check the Order of Magnitude by Rounding

In this worksheet, students check the order of magnitude of a calculation by rounding first.

'Check the Order of Magnitude by Rounding' worksheet

Key stage:  KS 3

Curriculum topic:   Number

Curriculum subtopic:   Use Calculators/Technology for Accuracy

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

When you use a calculator, you must have a rough idea of the expected size of your answer.

This size is called the order of magnitude and you can get a good idea by rounding off the question first.

 

7840 × 28 is approximately 8000 × 30 which is 240000

24216 - 18947 is approximately 24000 - 19000 = 5000

542 ÷ 18 is approximately 500 ÷ 20 or 25

 

Example

Let's find the order of magnitude for 3.42  × 19.

 

3.42 × 19 lies between
A
and
B
which equal 
C
and
D

 

3.42 × 19 lies between 3 × 19 and 4 × 19.

 

3.42 × 19 lies between
3 × 19
and
4 × 19
which equal 
57
and
76

 

 

Check to see how close you are by doing the calculation on your calculator as well.

 

3.42 × 19 =
64.98

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.98 × 21 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.98 × 21 =
E
 ABCDE
2 x 21
8 x 21
9 x 21
168
198
189
188.58

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

9.24 × 14 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

9.24 × 14 =
E
 ABCDE
9 x 14
8 x 14
10 x 14
129.36
198
140
126

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

3.46 × 22 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

3.46 × 22 =
E
 ABCDE
2 x 22
3 x 22
4 x 22
66
76.12
88

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

9.97 × 11 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

9.97 × 11 =
E
 ABCDE
8 x 11
9 x 11
10 x 11
109.67
99
110

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

7.02 × 10 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

7.02 × 10 =
E
 ABCDE
7 x 10
8 x 10
9 x 10
70
70.2
80

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

6.67 × 12 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

6.67 × 12 =
E
 ABCDE
6 x 12
7 x 12
8 x 12
80.04
72
84

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

5.01 × 13 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

5.01 × 13 =
E
 ABCDE
5 x 13
6 x 13
7 x 13
65
75
78
65.13

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

5.51 × 14 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

5.51 × 14 =
E
 ABCDE
5 x 14
6 x 14
7 x 14
70
75
84
77.14

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.32 × 22 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.32 × 22 =
E
 ABCDE
7 x 22
8 x 22
9 x 22
176
175
198
183.04

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.59 × 13 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.59 × 13 =
E
 ABCDE
7 x 13
8 x 13
9 x 13
104
115
117
111.67
  • Question 1

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.98 × 21 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.98 × 21 =
E
CORRECT ANSWER
 ABCDE
2 x 21
8 x 21
9 x 21
168
198
189
188.58
  • Question 2

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

9.24 × 14 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

9.24 × 14 =
E
CORRECT ANSWER
 ABCDE
9 x 14
8 x 14
10 x 14
129.36
198
140
126
  • Question 3

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

3.46 × 22 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

3.46 × 22 =
E
CORRECT ANSWER
 ABCDE
2 x 22
3 x 22
4 x 22
66
76.12
88
  • Question 4

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

9.97 × 11 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

9.97 × 11 =
E
CORRECT ANSWER
 ABCDE
8 x 11
9 x 11
10 x 11
109.67
99
110
  • Question 5

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

7.02 × 10 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

7.02 × 10 =
E
CORRECT ANSWER
 ABCDE
7 x 10
8 x 10
9 x 10
70
70.2
80
  • Question 6

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

6.67 × 12 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

6.67 × 12 =
E
CORRECT ANSWER
 ABCDE
6 x 12
7 x 12
8 x 12
80.04
72
84
  • Question 7

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

5.01 × 13 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

5.01 × 13 =
E
CORRECT ANSWER
 ABCDE
5 x 13
6 x 13
7 x 13
65
75
78
65.13
  • Question 8

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

5.51 × 14 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

5.51 × 14 =
E
CORRECT ANSWER
 ABCDE
5 x 14
6 x 14
7 x 14
70
75
84
77.14
  • Question 9

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.32 × 22 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.32 × 22 =
E
CORRECT ANSWER
 ABCDE
7 x 22
8 x 22
9 x 22
176
175
198
183.04
  • Question 10

Work out approximate answers to the following problem, stating the values of A, B, C, D and E.

 

8.59 × 13 lies between
A
and
B
which equal 
C
and
D

 

Check to see how close you are by doing the calculation on your calculator as well.

8.59 × 13 =
E
CORRECT ANSWER
 ABCDE
7 x 13
8 x 13
9 x 13
104
115
117
111.67
---- OR ----

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