In a packet of $500$ screws,$80$ screws are defective. Find the probability that a screw selected at random from the packet is non-defective. (in $/25$)

Find the probability that a leap year has $53$ Thursdays.

$A$ bag contains $24$ balls of which $x$ are red,$2x$ are white,and $3x$ are blue. $A$ ball is selected at random. What is the probability that it is:
$(i)$ not red?
$(ii)$ white?

$A$ card is drawn at random from a well-shuffled pack of $52$ cards. The probability of that card being an ace is ........

There are $5$ white, $7$ red, $4$ black, and $2$ blue identical balls in a box. One ball is selected at random from the box. Find the probability that the ball is either black or white.

There are $5$ red,$8$ white,and $4$ green balls in a box. $A$ ball is drawn at random from the box. Find the probability that the ball drawn is not green.