Four persons can hit a target correctly with probabilities $${1 \over 2}$$, $${1 \over 3}$$, $${1 \over 4}$$ and $${1 \over 8}$$ respectively. if all hit at the target independently, then the probability that the target would be hit, is :

The minimum number of times one has to toss a fair coin so that the probability of observing at least one head is at least 90% is :

Let A and B be two non-null events such that A $$ \subset $$ B . Then, which of the following statements is always correct?

In a class of 60 students, 40 opted for NCC, 30 opted for NSS and 20 opted for both NCC and NSS. If one of these students is selected at random, then the probability that the students selected has opted neither for NCC nor for NSS is :