All Years
1990 TYS
Question 7
Question

A circular card is divided into 3 sectors scoring 1, 2, 3 and having angles $135{}^\circ $, $90{}^\circ $, $135{}^\circ $ respectively. On a second circular card, sectors scoring 1, 2, 3, have angles $180{}^\circ $, $90{}^\circ $, $90{}^\circ $ respectively (see diagram). Each card has a pointer pivoted at its centre. After being set in motion, the pointers come to rest independently at random positions. Find the probability that
- the score on each card is 1.
- the score on at least one of the card is 3.
The random variable $X$ is the larger of the two scores if they are different, and their common value if they are the same. Show that $\text{P}\left( X=2 \right)=\frac{9}{32}$ . Show that $\text{E}\left( X \right)=\frac{75}{32}$ and find $\text{Var}\left( X \right)$.