Still on Proportion…

Published on ginnyent.net on 28th February, 2019

Example 3

Phosphor-bronze is a mixture of copper, tin and phosphorus in the ratio by mass 185:14:1. Find the mass of copper in a phosphor-bronze casting of mass 27.2kg.

Solution

Total ratio = 185 + 14 + 1

= 200

Mass of copper in the 27.2kg phosphor-bronze =

ratio of copper/total ratio × mass of the phosphor-bronze

= 185/200 × 27.2

Example 4

Two builders share 11 tonnes of brick so that one has one-and-half times as many as the other. The total cost is \$22, 750.00. How much does each pay?

Solution

Let their shares of the cost of the bricks be x and one-and-half of x;

If you change one-and-half into an improper fraction, you will have 3/2.

So their shares of the cost are 3/2 of x and x.

Total ratio = 5/2(x).

[Add the two shares to get 5/2(x)]

Now we are going to find x.

5/2(x) = \$ 22750

Make x the subject of the equation

x = \$22750 × 2

5

x = \$9100 [Answer]

So one builder pays \$9100; while the other builder pays:

3 /2(x) = 3 × 9100

2

= \$ 13, 650 [Answer]