Jenny sells "honey tea" to raise fund for homeless people. The probability of making a sale is, independently, 0.3 for each person she approaches.

a) Given that she approaches 10 people, find the probability that she will makes at most 3 sales. Interpret the value obtained.

b) What is the probability that she will makes the first sale at the fifth person she approaches?

c) What is the probability that she will makes 4 sales before the seventh person she approaches?

d) Based on Jenny's experience selling "honey tea" for the last 2 weeks, the probability that the person she approaches will buy 0,1,2 or more than 2 cups are 0.7, 0.15, 0.10 and 0.05 respectively. Jenny plans to approached 20 persons. What is the probability that 10 will not buy, will buy 1 cup, 4 will buy 2 cups and the rest will buy than 2 cups?