A plant breeder knows by experience that when he crosses 2 varieties of currant, 10% of the offspring will be disease-resistance, and that only 20% of the offspring will be sufficiently vigorous growers to warrant further trial. If he wishes to breed plants which are both vigorous and diseaseresistant, and these two characteristics are independent of one another;

a) What proportion of offspring will be of use to him?[5 Marks]