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Question -

Find the probability distribution of the number of successes in two tosses of a die, where a success is defined as
(i) number greater than 4
(ii) six appears on at least one die



Answer -

Given a die is tossedtwo 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.

(i) Here success isgiven as the number greater than 4.

Now

P (X = 0) = P (number≤ 4 in both tosses) = 4/6 × 4/6 = 4/9

P (X = 1) = P (number≤ 4 in first toss and number ≥ 4 in second case) + P (number ≥ 4 in first tossand number ≤ 4 in second case) is

= (4/6 × 2/6) + (2/6 ×4/6) = 4/9

P (X = 2) = P (number≥ 4 in both tosses) = 2/6 × 2/6 = 1/9

Hence, the requiredprobability distribution is,

X

0

1

2

P (X)

4/9

4/9

1/9

(ii) Here success isgiven as six appears on at least one 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

Hence, the requiredprobability distribution is,

X

0

1

P (X)

25/36

5/18

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