有个关于概率的数学题，求好心大神帮下忙！>.<

悠悠儿 · 发表于 2012-9-22 09:54:00

The proportion of American Express credit-card holders who pay their credit card bill in fulleach month is 20%; the other 80% make only a partial or no payment.(a) In a random sample of 15 customers, what is the probability that:i. 4 customers pay their bill in full? (2 marks)ii. More than 4 customers pay their bill in full? (2 marks)
Lifts usually have signs indicating their maximum capacity. Consider a sign in a lift that
reads “maximum capacity 1400kg or 20 persons”. Suppose that the weights of lift-users are
normally distributed with a mean of 65kg and a standard deviation of 10kg.
(a) What is the probability that a lift-user will weigh more than 70kg? (2 marks)
(b) What is the probability that a lift-user will weigh between 60 and 75kg? (2 marks)
(c) What is the probability that 20 people will exceed the weight limit of 1400kg? (3
marks)
(d) What is the probability that 25 people will not exceed the weight limit (Use Excel to
calculate probability to 6 decimal places)? (3 marks)

就这两题，求求知道的大神帮帮我~ QQ：41530881