L1 Numeracy Workbook Answers - Skills Workshop, 2011 Page 8
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32L1 Numeracy work book
Checking answers to calculations
Name_____________________
Checking your answers
There are two main methods:
1) Inverse calculation (doing the opposite calculation)
23 x 7= 161. To check: 161 ÷ 7 should lead you back to your first number of 23.
Try the following
Inverse
Check
565 + 563+ 301 =
864‐301=
301 864
563
457‐ 457‐21=
436+21=
21 436
457
£4.50 ÷ 50 £4.50 ÷ 50= 9p 9 x 50p = £4.50
45mm x 45mm x 38mm = 1710÷38 = 45
38mm 1710mm
2) Estimation
This is a “rough” check that ensures that you have not made any place value errors or
pressed the wrong key on a calculator.
To do this, use rounding.
For example: £22.75 +£19.78 = ? Estimate £20+£20= £40
Try the following
Round
Check
4.79 m x 5m
5m x 5m
£19.51 / £4.79
£20 ÷ £5
607mg + 487mg
600mg + 500mg
987 –5340 1000 – 5000 (to nearest thousand – 5300 to the
nearest hundred
October 2011. Answers kindly contributed by Kevin Melling and Judith White, Somerset Skills & Learning. Workbook written and contributed
by Simon Kelsey, Steps to Work. September 2011. Search for Simon, Kevin and Judith on
Adult Numeracy and Functional Maths. For related resources visit the download page for this resource at skillsworkshop
Page 8 of 32
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