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

3.2 Multiplying and dividing

To multiply and divide by 10, 100, 1000, etc., write the digits in their place value columns. To multiply, move the digits to the left (replacing the numbers on the right with zeros) and to divide move them to the right (putting in a decimal point, and any zeros necessary for the place value).

Multiplication and division by whole numbers in general can be carried out by combining this technique with a knowledge of the multiplication tables up to 10.

Example 12

A machine in a factory puts tops on bottles at the rate of 1 every second.

  • (a) How many bottles does it top in a 10 hour working day?

  • (b) How many bottles does it top in a 30 day month, at 10 hours a day?

Answer

  • (a) There are 60 seconds in a minute and so it puts on 60 tops a minute. There are 60 minutes in an hour so it puts on 60 × 60 tops in an hour, which gives 3600.

  • There are many ways to do this e.g. think of 60 × 60 as 6 × 10 × 6 × 10, which is 6 × 6 × 10 × 10, i.e. 36 × 100, giving 3600 as before.

  • However you tackle it, the important thing is to remember the place values of the numbers.

  • So it tops 3600 bottles an hour. In 10 hours it tops 3600 × 10 = 36 000 bottles.

  • It tops 36 000 bottles in a 10 hour day.

  • (b) To find out how many bottles it tops in 30 days, multiply 36 000 by 30.

  • This is 36 000 × 3 × 10 = 1 080 000.

  • So the factory machine tops 1 080 000 bottles a month (just over a million).

  • The factory puts on 1 080 000 bottle tops in 30 days.

MU120_4M1

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