Probability is defined as a measure of the likelihood of a required outcome happening.
This is given in fraction as: Probability=number of required outcome ÷ number of possible outcome.
Ex 1: There are 7 red balls, 8 white balls and 5 blue balls in a box. A ball is selected at random from the box. Find the probability that the ball is (a) White (b) Red (c) blue or red (d) neither red nor white (e) Green.
Total number of balls= 7 +8+5=20.
(a) Probability of picking a white ball= number of white balls÷total number of balls= 8÷20= 2\5.
(b)Probability of picking a red ball=no of red balls÷toal number of balls=7÷20= 7\20.
(C)blue or red= probability of red + probability of blue= (number of red balls + no of blue balls)÷ total number of balls=(7+5)÷20=12÷20=3\5.
(d)neither red nor white= probability of blue= number of blue balls ÷ total number of balls= 5÷20= 1\4.
(e) probability of picking a green ball= number of green balls÷ total number of balls=0÷20=0.

Ex 2: A tray of eggs contains 18 large-sized eggs and 12 small-sized eggs. An egg is selected at random. Find the probability of selecting (a) a small-sized egg (b)either a small-sized or a large-sized egg (c)neither a Small-sized nor a large-sized egg.
Total number of eggs= 18+ 12=30.
(a)probability of picking a small-sized egg=number of small-sized egg ÷total number of eggs=12÷30=2\5.
(b)probability of picking either a large-sized egg or small-sized egg=probability of large-sized egg + probability of small-sized egg=( number of large-sized egg + number of small-sized egg) ÷total number of egg=(18+12)÷30=30÷30=1.
(c)probability of picking neither a large-sized egg nor a small-sized egg= number of other sized egg÷ total number of eggs=0÷30=0.