$A$ bag contains $5$ red balls and some blue balls. If the probability of drawing a blue ball is double that of a red ball,determine the number of blue balls in the bag.

Why is tossing a coin considered to be a fair way of deciding which team should get the ball at the beginning of a football game?

$A$ piggy bank contains $100$ $50\, p$ coins,$50$ $Rs.\, 1$ coins,$20$ $Rs.\, 2$ coins,and $10$ $Rs.\, 5$ coins. If it is equally likely that one of the coins will fall out when the bank is turned upside down,what is the probability that the coin:
$(i)$ will be a $50\, p$ coin?
$(ii)$ will not be a $Rs.\, 5$ coin?

$A$ bag contains lemon flavoured candies only. Malini takes out one candy without looking into the bag. What is the probability that she takes out
$(i)$ an orange flavoured candy?
$(ii)$ a lemon flavoured candy?

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 $queen?$

It is given that in a group of $3$ students,the probability of $2$ students not having the same birthday is $0.992$. What is the probability that the $2$ students have the same birthday?