If 12 dice are thrown at a time, then the probability that a multiple of 3 does not appear on any dice is

In a class consisting of 40 boys and 30 girls. $30 \%$ of the boy and $40 \%$ of the girls are good at Mathematics. If a student selected at random from that class is found to be a girl, then the probability that she is not good at Mathematics is

A basket contains 12 apples in which 3 are rotten. If 3 apples are drawn at random simultaneously from it, then the probability of getting atmost one rotten apple is

7 coins are tossed simultaneously and the number of heads turned up is denoted by random variable $X$. If $\mu$ is the mean and $\sigma^2$ is the variance of $X$, then $\frac{\mu \sigma^2}{P(X=3)}=$