Unit 17 Section 1 : Estimating metric units

It is very useful to be able to estimate lengths, masses, etc. because it may not always be easy to measure them.

Some useful hints for estimating are listed below:
The height of a standard door is about 2 m.
The length of an adult pace is about 1 m.
The length of a size 8 shoe is about 30 cm.
Most adults are between 1.5 m and 1.8 m in height.
It takes about 15 minutes to walk one kilometre.
The mass of a standard bag of sugar is 1 kg.
The mass of a family car is about 1 tonne.
1 hectare = 10 000 m² (about 2 football pitches).
A teaspoon holds about 5 ml of liquid.
The volume of a normal can of drink is about 330 cm³.
Sometimes you can estimate by comparing one thing where you know the size with another where you don't.

Example Questions

Example Question 1
The picture below shows a tall man next to the front of a factory.

(a) Estimate the height of the factory in metres.
A tall man will probably be about 1.8 metres high.
We can see how many times taller the factory is than the man using the diagram below:

The factory is about five times as high as the man, so we multiply 1.8 metres by 5.
1.8m × 5 = 9m, so the height of the factory is about 9 metres.

(b) Estimate the height of the factory door in metres.
The door is taller than the man, but not twice as tall.
It is probably about 1½ times as tall, so we multiply 1.8 metres by 1½.
1.8m × 1½ = 2.7m, so the height of the factory door is a bit less than 3 metres.

Example Question 2
The picture below shows a car overtaking a lorry.

The car is 4.2 metres long and 2 metres high.

(b) Estimate the height of the lorry in metres.
The lorry is about three times taller than the car, so we multiply 2 metres by 3.
2m × 3 = 6m, so the height of the lorry is about 6 metres.

(b) Estimate the length of the lorry in metres.
The lorry is about twice as long as the car, so we multiply 4.2 metres by 2.
4.2m × 2 = 8.4m, so the length of the lorry is about 8½ metres.

Exercises

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Produced by A.J.Reynolds August 2008