Page 302 - Math Smart - 7

Ratio, rate and proportion

O The ratio of one quantity to another quantity tells us how much the first quantity Is as
compared to the second quantity.
No units are used when we write ratio.

Example
The ratio of 4 kg to 1 kg is written as 4 : 1, without any units.
O A ratio can be expressed In Its simplest form, like fractions.
O Equivalent ratios are found by multiplying or dividing each part of a ratio by the same number.
O Quantities can be expressed as a proportion of a whole. Proportion is a comparison of the
quantity of a part to the quantity of a whole.

Example
1 in every 4 pens is a red pen.
The proportion of red pens is T of the total number of pens.

If
O two quantities are in the same ratio, they are said to be in direct proportion.
The two quantities increase or decrease at the same rate.

10 machines ►90tovcars~^ [?^ ► 45
10 —^ 90
? machines -►45 toy cars [I] = i^lO = 5
90

Ratios used in building Mortar acts like a glue for

Builders use ratios when mixing cement, sand and aggregate. Different ratios holding building materials
are used to make mortar for bricklaying, for making concrete floors and for such as brick or stone
making bridges. together. It is made up of
a thick mixture of water.
Example
• 2 times as much sand as cement makes a good mortar for bricklaying.
• 4 times as much aggregate as cement makes a strong concrete to use
as a floor.
• For maximum strength, the volume of the water in the mix should be
4 times the mass of the cement.

Batching by High strength cement Coarse sand Stone Approximate yield

Bucket 1 bucket 2 2 buckets 2 2 buckets 4 buckets

Wheelbarrow 2 bags (1 bag = 50 kg) 2 2 wheelbarrows 2 2 wheelbarrows 0.26 m

Per m 7.7 bags (1 bag = 50 kg) 0.63 m 0.63 m

UNIT 13 Ratio, Rate and Proportion