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June 2014 p63 q3
2930
A pet shop has 6 rabbits and 3 hamsters. 5 of these pets are chosen at random. The random variable X represents the number of hamsters chosen.
Show that the probability that exactly 2 hamsters are chosen is \(\frac{10}{21}\).
Draw up the probability distribution table for X.
Solution
(i) To find the probability of choosing exactly 2 hamsters, we use combinations. The total number of ways to choose 5 pets from 9 is \(\binom{9}{5}\). The number of ways to choose 2 hamsters from 3 is \(\binom{3}{2}\), and the number of ways to choose 3 rabbits from 6 is \(\binom{6}{3}\).