$4$ coins are tossed once. Find the probability of getting exactly $2$ tails.

In a lottery,there were $90$ tickets numbered $1$ to $90$. Five tickets were drawn at random. What is the probability that two of the tickets drawn are numbered $15$ and $89$?

Study the given information carefully to answer the question that follows. An urn contains $4$ green,$5$ blue,$2$ red and $3$ yellow marbles. If $3$ marbles are drawn at random,what is the probability that none is green?

$A$ can hit a target $4$ times in $5$ shots,$B$ can hit a target $3$ times in $4$ shots,and $C$ can hit a target $2$ times in $3$ shots. All three fire a shot each. What is the probability that at least two shots hit the target?

Find the probability that in a random arrangement of letters of the word $'UNIVERSITY'$, two $I$s do not come together.

$A$ 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