White paint costs £2.80 per litre. Blue paint costs £3.50 per litre. White paint and blue paint are mixed in the ratio 3 : 2 Work out the cost of 18 litres of the mixture.

First it's importance to clarify what the question is asking: we're looking for the price of 18 litres of paint that is part white paint and part blue paint. One way to answer the question is to understand the ratio given in terms of percentages. The ratio 3:2 means that for every 3 units of white paint, we must mix 2 units of blue paint. Therefore, for a total 5 units (3+2) 3 of these must be white paint. Therefore, the white paint must make up 3 fifths or 60% of the mixture and the blue paint must make up 2 fifths or 40%. Therefore, out of the total 18 litres, 18 x 0.6 = 10.8, 10.8 litres should be white and 7.2 litres of blue paint should used. By multiplying these numbers by the price per litre for each paint we can work out the total cost: 10.8 x 2.80 = 30.24 7.2 x 3.50 = 25.2 total cost = 55.44