If $P(\overline{B}) = 0.81$,then $P(B) = \ldots$

In a game,the entry fee is $Rs. 5$. The game consists of tossing a coin $3$ times. If one or two heads show,Sweta gets her entry fee back. If she throws $3$ heads,she receives double the entry fee. Otherwise,she will lose. For tossing a coin three times,find the probability that she:
$(i)$ loses the entry fee.
$(ii)$ gets double the entry fee.
$(iii)$ just gets her entry fee back.

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?

Two balanced dice are rolled simultaneously. Then,the probability that the sum of numbers on the dice is $7$ is ............

Two balanced dice are rolled. Find the probability that the product of numbers on two dice is odd.

In a carton of $20$ bulbs,$4$ bulbs are defective. Find the probability that a bulb selected at random is non-defective.