If the probabilities of a boy and a girl being born are the same,then in a $4$-children family,the probability of having at least one girl is:

$A$ student appeared in an examination consisting of $8$ true-false type questions. The student guesses the answers with equal probability. The smallest value of $n$,so that the probability of guessing at least $n$ correct answers is less than $\frac{1}{2}$,is:

In order to get at least one head with a probability $\ge 0.9$,the minimum number of times a coin needs to be tossed is:

The incidence of occupational disease in an industry is such that the workmen have a $10 \%$ chance of suffering from it. The probability that out of $5$ workmen,$3$ or more will contract the disease is

The records of a hospital show that $10\%$ of the cases of a certain disease are fatal. If $6$ patients are suffering from the disease,then the probability that only three will die is

If the mean and variance of a binomial variable $X$ are $2$ and $1$ respectively, then $P(X \geq 1)$ is equal to