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Numbers, units and arithmetic
Numbers, units and arithmetic

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3.7.1 Try some yourself

Activity 38

Evaluate each of the following:

  • (a) 7.9 ×0.8

  • (b) 82.3 × 40

  • (c) 7.20 ÷ 0.8

  • (d) 62.30 ÷ 40

Answer

  • (a) 7.9 × 0.8 = 6.32

  •   (multiply by 8 then shift the digits one place to the right).

  • (b) 82.3 × 40 = 3292

  •   (multiply by 4 then shift the digits one place to the left).

  • (c)

  • (d)

Activity 39

Use your answer to question 1 above to evaluate the following.

  • (a) Special cheese is £7.90 per kilo. How much does 0.8 kilos cost?

  • (b) Petrol is 82.3p per litre. How much does 40 litres cost?

  • (c) The till receipt showed the cheese cost £7.20, and you bought 0.8 kilos. How much was it per kilo?

  • (d) The bill was £62.30 for 40 small children's party hats. How much were they each? Was there an error in the bill or a discount?

Answer

  • (a) 0.8 kilos of cheese costs 0.8 × £7.90 = £6.32.

  • (b) 40 litres of petrol costs 40 × 82.3p = 3292p = £32.92.

  • (c) The cheese costs £7.20 ÷ 0.8 = £9 per kilo.

  • (d) Each hat costs £62.30 ÷ 40 = £1.5575 each, but they must be a whole number of pence each so only two decimal places are meaningful. Hence there was either an error or some discount.