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Question -

Two dice are thrown simultaneously. If X denotes the number of sixes, find the expectation of X.



Answer -

Given a die is throwntwo times.

When a die is tossedtwo times then the number of observations will be (6 × 6) = 36.

Now, let X is a randomvariable which represents the success and is given as six appears on at leastone die.

Now

P (X = 0) = P (sixdoes not appear on any of die) = 5/6 × 5/6 = 25/36

P (X = 1) = P (sixappears at least once of the die) = (1/6 × 5/6) + (5/6 × 1/6) = 10/36 = 5/18

P (X = 2) = P (sixdoes appear on both of die) = 1/6 × 1/6 = 1/36

Hence, the requiredprobability distribution is,

X

0

1

2

P (X)

25/36

5/18

1/36

Therefore Expectationof X E (X):

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