A wine merchant mixes red and white wine in the ratio 7:3 by volume. He needs to prepare 50 litres of the mixture but realises the supplier only has 30 litres of red wine available. He will use all 30 litres of red and make up the remainder with white wine.
Calculate the ratio of red to white in the final 50 litre mixture, in simplest form.
(Total for Question 7 is 4 marks)