A tele-sales centre has found that 65% of the people they phone hang up before finding out what products are being sold. The salesmen call these "hang-ups". Sixty calls were made in the last 30 minutes.

a) What is the probability that half the calls were hang-ups?

b) What is the probability that 38 to 40 of the calls were hang-ups?

c) It is estimated that the tele-sales centre makes a loss of R10 for every hang-up. What is the expected loss for the sales made in the last 30 minutes?

d) What is the distribution of the random variable that gives the number of calls that are not hang-ups?