91Ó°ÊÓ

Adice is thrown twice and the sum of the numbers appearing is observed to be 6 . What is the conditional probability that the number 4 has appeared at least once?

The probability that a teacher will give an unannounced test during any class meeting is \(1 / 5\). If a student is absent twice, then the probability that the student will miss at least one test is (a) \(4 / 5\) (b) \(2 / 5\) (c) \(7 / 5\) (d) \(9 / 25\)

A coin is tossed \(n\) times. The probability of getting head at least once is greater than \(0.8\), then the least value of \(n\) is (a) 2 (b) 3 (c) 4 (d) 5

\(A\) can solve \(90 \%\) of the problem given in a book and \(B\) can solve \(70 \%\). What is the prob-ability that at least one of them will solve a problem selected at random from the book. [MP-99, 2003; CBSE-92(C)]

A man is known to speak the truth 3 out of 5 times. He throws a die and reports that it is a number greater than 4 . Find the probability that it is actually a number greater than 4 . [CBSE-2009]

A bag contains 30 balls numbered from 1 to 30; 1 ball is drawn randomly. The probability that the number of the ball is multiple of 5 or 7 is (a) \(1 / 2\) (b) \(1 / 3\) (c) \(2 / 3\) (d) \(1 / 4\)

Two cards are drawn one by one from a pack of cards. The probability of getting first card an ace and second a coloured one is (before drawing the second card the first card is not placed again in the pack) (a) \(\frac{1}{26}\) (b) \(\frac{5}{52}\) (c) \(\frac{5}{221}\) (d) \(\frac{4}{13}\)

In a box containing 100 eggs, 10 eggs are rotten. The probability that out of a sample of 5 eggs none is rotten if the sampling is with replacement is (a) \(\left(\frac{1}{10}\right)^{5}\) (b) \(\left(\frac{1}{5}\right)^{5}\) (c) \(\left(\frac{9}{5}\right)^{5}\) (d) \(\left(\frac{9}{10}\right)^{5}\)

A coin is tossed three times in succession. If \(E\) is the event that there are at least 2 heads and \(F\) is the event in which the first throw is a head, then \(P(E / F)=\) (a) \(3 / 4\) (b) \(3 / 8\) (c) \(1 / 2\) (d) \(1 / 8\)

If a party of \(n\) persons sits at a round table then the odds against two specified individuals sitting next to each other are (a) \(2:(n-3)\) (b) \((n-3): 2\) (c) \((n-2): 2\) (d) \(2:(n-2)\)