The probability that $A$ wakes up before the alarm rings is $0.4$. Then,the mean and variance of the number of times $A$ wakes up before the alarm rings,in the next $7$ days respectively are:

Suppose a machine produces metal parts that contain some defective parts with probability $0.05$. How many parts should be produced in order that the probability of at least one part being defective is at least $1/2$? (Given that,$\log_{10} 95 = 1.977$ and $\log_{10} 2 = 0.3$)

In a Binomial distribution with $n=4$,if $2 P(X=3)=3 P(X=2)$,then the variance is

If $X$ has a binomial distribution,$B(n, p)$ with parameters $n$ and $p$ such that $P(X = 2) = P(X = 3)$,then $E(X)$,the mean of variable $X$,is

$A$ radar system can detect an enemy plane in one out of $10$ consecutive scans. The probability that it cannot detect an enemy plane at least two times in four consecutive scans is:

At least how many times must a fair coin be tossed so that the probability of getting at least one head is at least $0.8$?