Probability – Exercise – 1

21. An unbiased die with faces marked 1, 2, 3, 4, 5 & 6 is rolled four times. Out of four face values obtained the probability that the minimum face value is not less that 2 and the maximum face value is not greater than 5, is :

(a) 16/81
(b) 1/81
(c) 80/81
(d) 65/81

22. A coin is tossed until a head appears or until the coin has been tossed five times. If a head does not occur on the first two tosses, then the probability that the coin will be tossed 5 times is :

(a) 1/2
(b) 3/5
(c) 1/4
(d) 1/3

23. The probabilities that A & B will die within a year are p & q respectively, then the probability that only one of them will be alive at the end of the year is :

(a) p + q
(b) P + q – 2qp
(c) p + q – pq
(d) p + p + pq

24. The letter of the word “ASSASSIN” are written down at random in a row. The probability that no two S occur together is :

(a) 1/35
(b) 1/14
(c) 1/15
(d) none of these

25. A bag A contains 2 white & 3 red balls & bag B contains 4 white & 5 red balls. One ball is drawn at random from a randomly chosen bag and is found to be red. The probability that it was drawn from bag B was :

(a) 5/14
(b) 5/16
(c) 5/18
(d) 25/52

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