Four persons entered the lift cabin on the ground floor f a 7 floor house. Suppose that each of them independently and with equal probability can leave the cabin at any floor beginning with the first. The probability of all 4 persons leaving at different floors is

An urn A contains 3 white and 5 black balls. Another urn B contains 6 white and 8 black balls. A ball is picked from A at random and then transferred to B. Then a ball is picked at random from B. The probability that it is a white ball is :

A, B, Care 3 news papers published from a city.20%of the population read A,16% read B,14% read C, 8% both A and C, 4% B and C,and2% read all the three. The percentage of then population who read at least one paper is

A bag contains 4 tickets numbered 1,2,3,4and another bag contains 6 tickets numbered 2,4,6,7,8,9. One bag is chosen and a ticket is drawn. The probability that the ticket bears the number 4 is

The odds that a book will be reviewed favorably by three independent critics are 5 to 2,4 to 3 and 3 to 4 respectively. The probability that of the three reviews amajority will be favourable is

A and B throw a pair of dice. A wins if he throw 6 before B throws 7 and B wins if he throws 7 before A throws 6. If A begins, his chance of winning is

There are 2 white, 4 black balls in urn A; In urn B, there are 5 white and 7 black balls. If one ball is randomly replaced from A into B , and a ball is drawn from B then the probabilty for the ball to be a white one is

An aircraft gun can take a maximum of three shots at an enemy plane moving away from it. The probabilities of hitting the plane at the first, second and third shot are 0.5,0.4,0.3 respectively. The probability that the gun hits the place is

Bag A contains 8 black and 5 white balls. Bag B contain 6 black and 7 white balls. A die is rolled. If 2 or 5 turns up, then choose bag A otherwise choosen B. If one ball is drawn from the selected bag, the probability that it is black is

Bag a contains 4white and 5 black balls. Bag b contains 5 white and 6 black balls. One bag is selected at random and a ball is drawn from it. The probability that it is white is