7.19 The proportions X1 and X2 of two chemicals found in samples of an insecticide have the joint probability density function The random variable Y  X1  X2 denotes the proportion of the insecticide due to both chemicals combined.

a Find E(Y) and V(Y ).

b Find an interval in which values of Y should lie for at least 50% of the samples of insecticide.

c Find the correlation between X1 and X2 and interpret its meaning.