Question

A pair of unbiased dice is rolled together till a sum of either 5 or 7 is obtained. The probability that 5 comes before 7 is

Solution

Correct option is

2/5

Let A denote the event that a sum of 5 occurs, B the event that a sum of 7 occurs and C the event that neither a sum of 5 nor a sum of 7 occurs. We have

         

Thus,

P (A occurs before B)

                 

                 

                 

                 

                 

SIMILAR QUESTIONS

Q1

Three six – faced fair dice are thrown together. The probability that the sum of the numbers appearing on the dice is 

k (3 ≤ k ≤ 8) is

Q2

If the mean and variance of a binomial variate X are 2 and 1 respectively, then the probability that X takes values at most 3 is

Q3

If two events A and B such that P(A’) = 0.3, P(B) = 0.5 and P(A  B) = 0.3, then  is

Q4

Seven white bails and three black balls are randomly placed in a row. The probability that no two black balls are placed adjacently equals

Q5

If from each of the three boxes containing 3 white and 1 black, 2 white and 2 black, 1 white and 3 black balls, one ball is drawn at random, then the probability that two white and one black ball will be drawn is

Q6

There are four machines and it is known that exactly two of them are faulty. They are tested, one by one, in a random order till both the faulty machines are identified. Then the probability that only two tests are needed is

Q7

A group of 2n boys and 2n girls is randomly divided into two equal groups. The probability that each group contains the same number of boys and girls is

Q8

Let A and B be two events such that P(A) = 0.3 and P(A  B) = 0.8. If Aand B are independent events, then P(B) is

Q9

An unbiased dia with faces marked 1, 2, 3, 4, 5 and 6 is rolled four times out of the four faces obtained, the probability that the minimum value is exactly than 2 and the maximum value is exactly 5 is

Q10

Each of two persons A and B toss three fair coins. The probability that both get the same number of heads is