$A$ jar contains $24$ marbles,some are green and others are blue. If a marble is drawn at random from the jar,the probability that it is green is $\frac{2}{3}$. Find the number of blue balls in the jar.

There are boards numbered $1$ to $50$ in a box. One board is selected at random. Find the probability that the number on the board is a multiple of $11$. (in $/25$)

Which of the following cannot be the probability of an event?

Five cards - the ten,jack,queen,king and ace of diamonds,are well-shuffled with their face downwards. One card is then picked up at random.
$(i)$ What is the probability that the card is the queen?
$(ii)$ If the queen is drawn and put aside,what is the probability that the second card picked up is $(a)$ an $ace?$ $(b)$ a $queen?$

Two unbiased dice are thrown once. Write all the possible outcomes of this experiment. What is the probability that the sum of numbers on two dice is a prime number?

The probability of the month of February in a leap year having $5$ Fridays is ..........