Question

Find the probability distribution of the maximum of the two scores obtained when a die is thrown twice. Determine also the mean of the distribution.

Answer 1

Let X be the random variable scores when a die is thrown twice.

X = 1, 2, 3, 4, 5, 6

And S = {(1, 1), (1, 2), (2, 1), (2, 2), (1, 3), (2, 3), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), ..., (6, 6)}

So, P(X = 1) = `1/6*1/6 = 1/36`

P(X = 2) = `1/6*1/6 + 1/6*1/6 + 1/6*1/6 = 3/36`

P(X = 3) = `1/6*1/6 + 1/6*1/6 + 1/6*1/6 + 1/6*1/6 + 1/6*1/6 = 5/36`

Similarly P(X = 4) = `7/36`

P(X = 5) = `9/36`

And P(X = 6) = `11/36`

So, the required distribution is

X	1	2	3	4	5	6
P(X)	`1/36`	`3/36`	`5/36`	`7/36`	`9/36`	`11/36`

Now, the mean E(X) = `sum_("i" = 1)^"n" x_"i""p"_"i"`

= `1 xx 1/36 + 2 xx 3/36 + 3 xx 5/36 + 4 xx 7/36 + 5 xx 9/36 + 6 xx 11/36`

= `1/36 + 6/36 + 15/36 + 28/36 + 45/36 + 66/36`

= `161/36`

Hence, the required mean = `161/36`.