CBSE Guess > Papers > Important Questions > Class XII > 2010 > Maths > Mathematics By Mr Vasu Raj CBSE CLASS XII
Q. 11. If A and B are two independent events, then the probability of occurrence of at least one of A and B is given by 1– P(A′) P(B′) 3. A box of oranges is inspected by examining three randomly selected oranges drawn without replacement. If all the three oranges are good, the box is approved for sale, otherwise, it is rejected. Find the probability that a box containing 15 oranges out of which 12 are good and 3 are bad ones will be approved for sale. Ans. 44/91 Q. 13. Two balls are drawn at random with replacement from a box containing 10 black and 8 red balls. Find the probability that (i) both balls are red. (ii) first ball is black and second is red. (iii) one of them is black and other is red. Ans. 16/81, 20/81, 40/81 Q. 14. Probability of solving specific problem independently by A and B are ½ and 1/3 respectively. If both try to solve the problem independently, find the probability That Ans. 2/3, 1/2 Q. 15. In a hostel, 60% of the students read Hindi news paper, 40% read English news paper and 20% read both Hindi and English news papers. A student is selected at random. Ans. 1/5, 1/3, 1/2. Q. 16. Suppose that the reliability of a HIV test is specified as follows: Of people having HIV, 90% of the test detect the disease but 10% go undetected. Of people free of HIV, 99% of the test are judged HIV–ive but 1% are diagnosed as showing HIV+ive. From a large population of which only 0.1% have HIV, one person is selected at random, given the HIV test, and the pathologist reports him/her as HIV+ive. What is the probability that the person actually has HIV? Ans. 0.083 Q. 17. A man is known to speak truth 3 out of 4 times. He throws a die and reports that it is a six. Find the probability that it is actually a six. Ans. 3/8 Q. 18. Suppose a girl throws a die. If she gets a 5 or 6, she tosses a coin three times and notes the number of heads. If she gets 1, 2, 3 or 4, she tosses a coin once and notes whether a head or tail is obtained. If she obtained exactly one head, what is the probability that she threw 1, 2, 3 or 4 with the die? Ans. 8/11 Q. 19. Probability that A speaks truth is4/5 . A coin is tossed. A reports that a head appears. What is the probability that actually there was head. Ans. 4/5 Q. 20 Two cards are drawn successively with replacement from a well-shuffled deck of 52 cards. Find the probability distribution of the number of aces. Ans.
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