Question

an urn contains white ,black and red balls only. a ball is drawn at random from the bag . the probability of getting a white ball is 3/10 and that of a black ball is 2/5 . find the probability of getting a red ball . if the bag contains 20 black balls ,then find the total no. of balls in the bag.

Answer 1

Let the total no. of balls be x

Probability of drawing a black ball = 2/5 (given)

20/x = 2/5

x = 50 = no.of balls

Let no. of white balls be y

Now Probability of getting a white ball = 3/10 (given)

y/50 = 3/10

y = 15

Thus,No.of red balls = 50-(20+15)

= 50-35

= 15

Therefore, Probability of getting a red ball = 15/50

= 3/10