8.49 Rules for means and variances. It is quite easy to verify the formulasfor the mean and standard deviation of the difference D.

1. (a) What are the means and standard deviations of the two sample proportions and ?

2. (b) Use the addition rule for means of random variables: what is the mean of ?

3. (c) The two samples are independent. Use the addition rule for variances of random variables: what is the variance of D?