7.19. A GSS reported that the 486 females had a mean of 8.3 close friends (s = 15.6) and the 354 males had a mean of 8.9 close friends (.s = 15.5).

(a) A 95% confidence interval for the difference between the population means for males and for females is (-1.5, 2.7). Interpret.

(b) For each sex, does it seem like the distribution of number of close friends is normal?

Explain why this does notinvalidate the result in (a), but may affect the usefulness of the interval.