Numbers, units and arithmetic
Numbers, units and arithmetic

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Numbers, units and arithmetic

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


  • (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?


  • (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.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371