In a throw of a die, what is the probability of getting a number less than $7$

Describe the sample space for the indicated experiment: A coin is tossed four times.

A locker can be opened by dialing a fixed three digit code (between $000$ and $999$). A stranger who does not know the code tries to open the locker by dialing three digits at random. The probability that the stranger succeeds at the ${k^{th}}$ trial is

The probability of hitting a target by three marksmen are $\frac{1}{2},\,\frac{1}{3}$ and $\frac{1}{4}$ respectively. The probability that one and only one of them will hit the target when they fire simultaneously, is

One card is drawn from a well shuffled deck of $52$ cards. If each outcome is equally likely, calculate the probability that the card will be a black card (i.e., a club or, a spade)