 # Check the Order of Magnitude by Rounding

In this worksheet, students check the order of magnitude of a calculation by rounding first. Key stage:  KS 3

Curriculum topic:   Number

Curriculum subtopic:   Use Calculators/Technology for Accuracy

Difficulty level:   ### 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 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
 A B C D E 7 x 13 8 x 13 9 x 13 104 115 117 111.67
---- OR ----

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