SMILE
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Unit 7: Numeracy skills

Decimals

Rounding up

Some decimal numbers go on for ever! To simplify their use, we decide on a cut off point and “round” them up or down.

If we want to round 2.734216 to two decimal places, we look at the number in the third place after the decimal, in this case, 4. If the number is 0, 1, 2, 3 or 4, we leave the last figure before the cut off as it is. If the number is 5, 6, 7, 8 or 9 we “round up” the last figure before the cut off by one. 2.734216 therefore becomes 2.73 when rounded to 2 decimal places.

If we are rounding to 2 decimal places, we leave 2 numbers to the right of the decimal.
If we are rounding to 2 significant figures, we leave two numbers, whether they are decimals or not.

Example 1

2 4 3 .7 6 8 4 = 243.77 (two decimal places)
              = 240 (two siginificant figures)

1 9 7 3 . 2 8 5 = 1973.29 (2 decimal places)
                = 2000 (2 siginificant figures)
question mark
2 . 4 6 8 9 = 2.47 (two decimal places)  
            = 2.5 (two siginificant figures)  

0 . 9 9 8 7 9 = 1.00 (2 decimal places)
              = 1.0 (2 significant figures)

Try these examples. Give all your answers to 2 decimal places and 2 significant figures
1. 2.45 + 7.68 2. 3.17 + 12.15 3. 2.421 + 13.1
4. 162.5 + 2.173 5. 12.5 – 3.7 6. 9.6 – 7.8
7. 163.5 – 2.173 8. 2.416 – 1.4 9. 26.95 – 1.273
10. 1.5 x 7.2 11. 2.73 x 8.14 12. 6.25 x 17 x 3
13. 2.96 x 17.3 14. 4.2 / 1.7 15. 53.9 / 2.76
16. 14.2 / 6.1 17. 2.5 / 0.03 18. 250/2.35
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SMILE - Numeracy skills by Tom Frank, Eric Williams and Clare Wright, University of Birmingham Careers Centre adapted by Marion Kelt Glasgow Caledonian University is licensed under a Creative Commons Attribution 3.0 Unported License.