The probability that event $A$ happens in a trial is $0.4$. If three independent trials are made, then the probability that $A$ happens at least once is.......

When employees with smart phones are randomly selected,$50 \%$ use them for office purpose. The probability that out of $10$ users exactly $2$ of them use for office purpose is

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

$A$ multiple choice examination has $5$ questions. Each question has three alternative answers of which exactly one is correct. The probability that a student will get $4$ or more correct answers just by guessing is

$A$ fair coin is tossed a fixed number of times. If the probability of getting five heads is equal to that of getting seven heads, then the probability of getting four heads is

The items produced by a firm are supposed to contain $5\%$ defective items. The probability that a sample of $8$ items will contain less than $2$ defective items is: