Question:A motor-cyclist mixes oil and petrol in the ratio 1:20. If petrol costs 9p per litre and oil 19 `1/2`p per litre, find the cost of a litre of the mixture.
Answer
Consider any convenient volumes in the ratio 1:20, e.g 1 litre of oil and 20 litre of petrol. 20 liters of petrol cost 20 x 9p = £1.80 1 liters of oil costs 1 x 19`1/2`p = £`0.19 1/2` Total cost of 21 liters of mixture = £1.99`1/2` Average cost per litre of mixture = `(£1.99 1/2)/21 = (199.1/2p)/21 = 9 1/2p`