Unit 19 Section 1 : Measuring Lengths
In this section we consider which units to use and the errors made when measuring lengths.
We need to be able to use millimetres (mm), centimetres (cm), metres (m) and kilometres (km).
Appropriate Units
Work out which unit of length (mm, cm, m or km) would be most appropriate for
measuring each item below, then click
to see whether you are correct.
(a) Your height?
(b) The height of a block of flats?
(c) The length of your foot?
(d) The thickness of your maths book?
(e) The distance between your school and the nearest other school?
Errors in measurement
It is difficult to measure any length completely accurately.
When we measure a person's height, we normally measure it to the nearest centimetre.
Example
A person's height was measured as 163cm (to the nearest cm).
What range of values could that person's actual height have been?
The height must be 162.5 cm or more because a lower height would have rounded down to 162 cm.
The height must be less than 163.5 cm because 163.5 cm would have been rounded up to 164 cm.
The lowest possible height would have been 162.5 cm. We call this the lower bound.
The actual height must have been less than 163.5 cm. We call this the upper bound.
Practice Question
A line is measured to the nearest centimetre as 12 cm.
(a) What is the shortest possible length of this line?
(b) What length must the actual length of the line be less than?
Exercises
Work out the answers to the questions below and fill in the boxes. Click on the
button to find out whether you have answered correctly. If you are right
then will appear and you should move on to the next
question. If appears then your answer is wrong. Click
on to clear your original answer and have another go.
If you can't work out the right answer then click on
to see
the answer.
You have now completed Unit 19 Section 1
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Produced by A.J.Reynolds January 2001