Question

A box containing 3 red, 3 white and 3 green balls. A ball is selected at random. Find the probability that,

(i) ball picked up is a red ball.

Answer 1

One ball is drawn at random from a bag containing 3 red balls (R1, R2 and R3), 3 white balls (W1, W2 and W3) and 3 green balls (G1, G2 and G3).
∴ S = {R1, R2, R3, W1, W2, W3, G1, G2, G3}
Or,
n(S) = 9

(i) Now, A is the event that the picked ball is a red ball.
∴ A = {R1, R2, R3}
Or,
n(A) = 3
Thus, we have:
P(A) = $\frac{n\left(\mathrm{A}\right)}{n\left(\mathrm{S}\right)}=\frac{3}{9}=\frac{1}{3}$