Numbers, units and arithmetic

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# 2.1 Which units to use

It is important to choose appropriate units, both to have a sense of the size you are talking about and also to avoid having to deal with very large or very small numbers.

For example using the UK decimal system, where £1 = 100p (one pound is equivalent to 100 pence), you would probably use pence for prices less than a pound: 50p rather than £0.50 and pounds for larger amounts, e.g. £2.50 instead of 250p.

For distance, mass and liquid measures, the metric system of units is often used. For example, the distance a cyclist cycles in a day is likely to be given in kilometres (sometimes written as the symbol km), a person's height in metres (m) and a waist measurement in centimetres (cm). The prefixes ‘kilo’ and ‘centi’, together with ‘deci’ and ‘milli’, are used throughout the metric system. Some common prefixes are shown in Table 1.

## Table 1: Prefixes used in the decimal system

Prefix Symbol Meaning Factor
micro- μ one millionth 0.000001
milli- m one thousandth 0.001
centi- c one hundredth 0.01
deci- d one tenth 0.1
kilo- k thousand 1000
mega- M million 1 000 000
giga- G thousand million 1 000 000 000

So 1 centimetre = metre or 1 cm = m.

This is the same as saying there are 100 centimetres in 1 metre or 100 cm = 1 m.

For mass, kilograms (kg), grams (g) or milligrams (mg) are usually used and a metric tonne is used for very large masses (1000 kg). The word ‘mass’ is scientifically more precise than ‘weight’, although people usually talk about weight rather than mass. For liquid capacity, litres (l), decilitres (dl), centilitres (cl) or millilitres (ml) are used.

MU120_4M1

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The text passage provides an overview of the importance of choosing appropriate units for different types of measurements, including currency, distance, mass, and liquid capacity, and introduces common metric prefixes.
no_question
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
Numbers, units and arithmetic

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

# 2.1 Which units to use

It is important to choose appropriate units, both to have a sense of the size you are talking about and also to avoid having to deal with very large or very small numbers.

For example using the UK decimal system, where £1 = 100p (one pound is equivalent to 100 pence), you would probably use pence for prices less than a pound: 50p rather than £0.50 and pounds for larger amounts, e.g. £2.50 instead of 250p.

For distance, mass and liquid measures, the metric system of units is often used. For example, the distance a cyclist cycles in a day is likely to be given in kilometres (sometimes written as the symbol km), a person's height in metres (m) and a waist measurement in centimetres (cm). The prefixes ‘kilo’ and ‘centi’, together with ‘deci’ and ‘milli’, are used throughout the metric system. Some common prefixes are shown in Table 1.

## Table 1: Prefixes used in the decimal system

Prefix Symbol Meaning Factor
micro- μ one millionth 0.000001
milli- m one thousandth 0.001
centi- c one hundredth 0.01
deci- d one tenth 0.1
kilo- k thousand 1000
mega- M million 1 000 000
giga- G thousand million 1 000 000 000

So 1 centimetre = metre or 1 cm = m.

This is the same as saying there are 100 centimetres in 1 metre or 100 cm = 1 m.

For mass, kilograms (kg), grams (g) or milligrams (mg) are usually used and a metric tonne is used for very large masses (1000 kg). The word ‘mass’ is scientifically more precise than ‘weight’, although people usually talk about weight rather than mass. For liquid capacity, litres (l), decilitres (dl), centilitres (cl) or millilitres (ml) are used.

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 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
user
The text passage provides an overview of the importance of choosing appropriate units for different types of measurements, including currency, distance, mass, and liquid capacity, and introduces common metric prefixes.

TYPE: NO_QUESTION