Everyday maths for Construction and Engineering 1

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# 3.2 Comparing weights

By law, weights of goods for sale in the UK have to be in metric units: grams and kilograms.

Historically, however, most people used imperial measures of weight: in size order these are ounces, pounds and stones.

• 16 ounces (oz) = 1 pound (lb)
• 14 pounds = 1 stone (st)

You might still come across these weights sometimes.

An ounce is a bit less than 30 g. A pound is a bit less than half a kilogram.

## Example: Two weight measurements

You have an old ladder with a label that says it can hold up to 20 stone. You weigh 80 kg. Can you safely use the ladder?

Hint: 1 st = 14 lb

### Method

You need to work out roughly what 20 stone is in kilograms. First, you need to find out how much 20 stone is in pounds.

• 20 × 14 = 280 lbs

One pound is equivalent to nearly half a kilogram, so next you need to divide the weight in pounds by 2:

• 280 ÷ 2 = 140

Now try the following activity. Remember to check your answers once you have completed the questions.

## Activity 8: Converting weights

1. An airline’s weight allowance for a piece of hand luggage is 5 kg. You have weighed your bag on some old bathroom scales and found that it is 7 lbs. Can you take it?
2. You have been told by the site foreman that you need to use 4 oz of grout. You have only 150 g left. Do you have enough?

1. A pound is a bit less than half a kilogram. To estimate what the weight allowance is in pounds, you need to multiply the amount in kilograms by 2:
• 5 × 2 = 10 lbs

Alternatively, you could estimate how much your bag weighs in kilograms by dividing the amount in pounds by 2:

• 7 ÷ 2 = 3.5 kg

Using either method, your bag doesn’t exceed the weight allowance.

1. An ounce is a bit less than 30 g. To estimate how much grout you need in ounces, you need to multiply the amount in ounces by 30:
• 4 × 30 = 120 g

Alternatively, you could estimate how much grout you have in ounces by dividing the amount in grams by 30:

• 150 ÷ 30 = 5 oz

Using either method, you have enough grout for the job.

## Summary

In this section you have learned how to:

• estimate and measure weight
• use metric units of weight
• know the relationship between grams and kilograms
• convert from imperial to metric units of weight.
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