Use the absolute deviation and avoid double-counting the double-two case

X has the following distribution.

x	$P(X=x)$
2	0.2
3	a
4	b
5	0.45

Given $E(|X-4|)=11/10$, find a and b.3 marks

Two independent observations of X are taken. Find the probability that one is 2 and the other is at most 4.2 marks