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Question -

Two numbers are selected at random (without replacement) from the first six positive integers. Let X denote the larger of the two numbers obtained. Find E(X).



Answer -

Given first sixpositive integers.

Two numbers can beselected at random (without replacement) from the first six positive integer in6 × 5 = 30 ways.

X denote the larger ofthe two numbers obtained. Hence, X can take any value of 2, 3, 4, 5 or 6.

For X = 2, thepossible observations are (1, 2) and (2, 1)

P (X) = 2/30 = 1/15

For X = 3, thepossible observations are (1, 3), (3, 1), (2, 3) and (3, 2).

P (X) = 4/30 = 2/15

For X = 4, thepossible observations are (1, 4), (4, 1), (2,4), (4,2), (3,4) and (4,3).

P (X) = 6/30 = 1/5

For X = 5, thepossible observations are (1, 5), (5, 1), (2,5), (5,2), (3,5), (5,3) (5, 4) and(4,5).

P (X) = 8/30 = 4/15

For X = 6, thepossible observations are (1, 6), (6, 1), (2,6), (6,2), (3,6), (6,3) (6, 4),(4,6), (5,6) and (6,5).

P (X) = 10/30 = 1/3

Hence, the requiredprobability distribution is,

X

2

3

4

5

6

P (X)

1/15

2/15

1/5

4/15

1/3

Therefore E(X) is:

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