Browsing as Guest. Progress, bookmarks and attempts are disabled.
Log in to track your work.
Nov 2014 p63 q7
2928
A box contains 2 green apples and 2 red apples. Apples are taken from the box, one at a time, without replacement. When both red apples have been taken, the process stops. The random variable X is the number of apples which have been taken when the process stops.
Show that \(P(X = 3) = \frac{1}{3}\).
Draw up the probability distribution table for \(X\).
Another box contains 2 yellow peppers and 5 orange peppers. Three peppers are taken at random from the box without replacement.
Given that at least 2 of the peppers taken from the box are orange, find the probability that all 3 peppers are orange.
Solution
(i) To find \(P(X = 3)\), we consider the sequences where the process stops after 3 apples. The sequences are GRR and RGR. The probability for GRR is \(\frac{2}{4} \times \frac{2}{3} \times \frac{1}{2} = \frac{1}{6}\). The probability for RGR is \(\frac{2}{4} \times \frac{2}{3} \times \frac{1}{2} = \frac{1}{6}\). Therefore, \(P(X = 3) = \frac{1}{6} + \frac{1}{6} = \frac{1}{3}\).
(ii) The probability distribution table for \(X\) is:
X
2
3
4
Prob
\(\frac{1}{6}\)
\(\frac{1}{3}\)
\(\frac{1}{2}\)
(iii) To find the probability that all 3 peppers are orange given that at least 2 are orange, we use conditional probability:
\(P(3 \text{ orange } | \text{ at least 2 orange }) = \frac{P(3 \text{ orange })}{P(\text{at least 2 orange})}\).