Page 50 - Mathematics Coursebook

4.2 Choosing suitable units

4.2 Choosing suitable units

You should always choose appropriate units of measurement to
measure and estimate length, mass and capacity.

Worked example 4.2

a Which units would you use to measure:
i the height of a chair ii the mass of a dog?
b Ajani estimates the height of the door in his classroom to be 1.4 m.
Is this estimate sensible? Give a reason for your answer.

a i cm A chair is usually less than 1 m high, so centimetres would be the best unit to use.
ii kg Most dogs weigh more than 1 kg, so kilograms would be the best unit to use.
b No, an average adult is about 1.7 m tall, so 1.4 m would be too small.
Compare Ajani’s estimate with a height that you know then make a decision and
give a reason.

) Exercise 4.2

1 Which metric units would you use to measure the following?
a the length of a football pitch b the mass of an apple
c the mass of an adult elephant d the capacity of a mug
e the width of a pencil f the mass of a person
g the length of this maths book h the capacity of the petrol
tank of a car

2 Which measurement, A, B or C, do you think is most likely to be the correct one for each object?
a the width of a computer screen A 32 mm B 32 cm C 32 m
b the mass of a banana A 20 g B 2 kg C 200 g
c the capacity of a bucket A 5 l B 50 l C 50 ml
d the height of a bus A 300 mm B 30 m C 3 m
e the capacity of a teaspoon A 500 ml B 5 l C 5 ml
f the mass of a horse A 600 kg B 6 t C 60 kg
3 Jayla has a brother who is 8 years old. She estimates his weight to be 65 kg. Is this estimate sensible?
Give a reason for your answer.

4 Deion has a new pencil. He estimates that the length of the pencil is 16 cm. Is this estimate sensible?
Give a reason for your answer.

5 Jamar has these cards.
10
80 m mass of a full suitcase 1

capacity of a can of cola cm
330 g length of a toothbrush

kg length of a house 25

mass of a mobile phone 18 capacity of a bath tub ml 125
Sort the cards into their correct groups. Each group must contain one green, one pink
and one blue card.
4 Length, mass and capacity 4 Length, mass and capacity 49