Rounding and estimation
Rounding and estimation

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Rounding and estimation

1.4.1 Try some yourself

Activity 5

Round a measurement of 1.059 metres:

  • (a) to the nearest whole number of metres;

  • (b) to two decimal places;

Answer

  • (a) 1.059 m rounded to the nearest whole number of metres is 1 m.

  • (b) 1.059 m rounded to two decimal places is 1.06 m.

Activity 6

Round each of the numbers below to:

  • (a) to 1 d.p.

  • (b) to 2 d.p.

  • (c) to 3 d.p.

  0.472 65,  13.959 943,  56.098 27

Answer

  • (a) 0.5,  14.0,  56.1

  • (b) 0.47,  13.96,  56.10

  • (c) 0.473,  13.960,  56.098

Activity 7

The table below contains some errors. Identify them and write down the correct rounding.

Rounded to
Number 1 d.p. 2 d.p. 3 d.p.
3.141 592 6 3.10 3.14 3.150
22/7 3.1 3.04 3.142
0.019 999 0.0 0.19 0.200

Answer

The corrected entries are in bold.

Rounded to
Number 1 d.p. 2 d.p. 3 d.p.
3.141 592 6 3.1 3.14 3.142
22/7 3.1 3.14 3.143
0.019 999 0.0 0.02 0.020

Activity 8

Imagine you are alone on an island and that your only source of drinking water is a wrecked ship's full water tank. It measures 4 metres long by 3.45 metres wide and is 2.84 metres high. Use reasonable rounded values to make an estimate (without using your calculator) of how long you can survive until it rains, assuming that you need 2 litres per day and that the water remains perfectly fresh. You may need the conversion 1 cubic metre contains 1000 litres. (Note that volume = length × width × height.)

Answer

Rounding to approximate accuracy and then calculating the volume of the tank by using the formula length × width × height gives a volume of approximately 4 × 3 × 3 = 36 cubic metres. 1 cubic metre contains 1000 litres, so 36 cubic metres contains 36 × 1000 = 36 000 litres.

If you need 2 litres per day of water then you can survive 36 000 ÷ 2 = 18 000 days before it rains. This is about 20 000 days and taking a year to be about 400 days means that you can survive about 20 000 ÷ 400 = 50 years.

The accurate answer would give 53.69 years (to 2 d.p.). You might not be too concerned to be told that you had only 50 years rather than 53.69 years to live on your deserted island if it did not rain!

MU120_4M2

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 over 40 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, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 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 prospectus