好深既statictics 1 --- probability

我對於statistics 真係好唔掂, 下面呢8題有無高手識做?? 可以教教我, 求求你們 ~~ 10萬個唔該

1. 42% of a corporation’s blue-collar employees were in favour of a modified health care plan, and 22% of its blue-collar employees favoured a proposal to change the work schedule. 34% of those favouring the health plan modification favoured the work schedule change.

a. What is the probability that a randomly selected blue-collar employee is in favour of both the modified health plan and the changed work schedule?
b. What is the probability that a randomly chosen blue-collar employee is in favour of at least one of the two changes?
c. What is the probability that a blue-collar employee favouring the work schedule change also favours the modified health plan?


2. A mail-order firm considers three possible events in filling an order:

A: The wrong item is sent.
B: The item is lost in transit.
C: The item is damaged in transit.

Assume that A is independent of both B and C and that B & C are mutually exclusive. The individual event probabilities are P(A) = 0.02, P(B) = 0.01, and P(C) = 0.04. Find the probability that at least one of these foul-ups occurs for a randomly chosen order.



3. In a promotion for a particular airline, customers and potential customers were given vouchers. A 1/400 proportion of these were worth a free round trip ticket anywhere this airline flies. How many vouchers would an individual need to collect in order to have a 50% chance of winning at least one free trip?