There is a bag that contains only red and blue marbles. The
probability of choosing a red
marble at random is 2/7. Given
that there are 12 red marbles in
total, and each one is likely to be
chosen at random work out out
how many marbles there must be
in total.
Your answer

Among the most famous of all meteor showers are the perseids, which occur each year in early august. in some areas the frequency of visible perseids can be as high as 40 per hour. given that such sightings are poisson events, calculate the probability that an observer who has just seen a meteor will have to wait at least five minutes before seeing another.