A box contains 5 white and 4 black balls. Two balls are picked together at random from the box.

What is the probability that these two balls are of different colours ?

1.          1/2
2.          5/18
3.          5/9
4.          1/3

If the integers m and n are chosen at random from 1 to 100, then the probability that a number of the from 7n + 7m is divisible by 5 equals

Ottawa's Confederation Line trains arrive at peak times at a station
to a station on a Poisson basis, averaging 10 trains per hour.
1. What is the waiting time distribution of three trains? What is the
What is the probability that this waiting time is at most 25 minutes? What
What are the mean and variance of this random variable?
2. No train arrives during the first 5 minutes of waiting. What is the
What is the probability that there will be no train during the next 3 minutes?
3. What is the probability that two trains will arrive in twelve minutes?
4. At 95%, at least one train arrives in t-minutes. What is approximately
t in minutes?
5. A period of 5 minutes is said to be empty if it contains no arriving
of trains. What is the probability that at most one 5-minute period
is empty in one hour?

Question 10 The weekly demand for a product approximately has a normal distribution with mean 1,000 and standard deviation 200. The current on hand inventory is 2,200 and no deliveries will be occurring in the next two weeks. Assuming that the demands in different weeks are independent,
a) What is the probability that the demand in each of the next 2 weeks is less than 1,100?
b) What is the probability that the total of the demands in the next 2 weeks exceeds 2,200?