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.

To work out how many litres of white and blue paint is needed, use the ratio 3:2. To find the specifc ratio for 18 litres, of paint: 2+3=5, 18/5=3.6 so (3:2)3.6 becomes 10.8:7.2 (check 10.8+7.2=18). So to determine the cost multiply the cost per litre by how many  litres were used of each paint: 2.810.8+3.5*7.2=30.24+25.2=  £55.44