Question

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

Answer 1

Black balls = 20

P(E) white ball = 3/10

P(E) black ball = 2\5 = 20\50

∴ Total balls = 50

Total balls = 50

White balls = 3*5\10*5 = 15\50

∴ White balls = 15

Red balls = 50 - (30+15)

Red balls = 5

Answer 2

Answer:

P(red) = 3 / 10

There are 50 balls in the bag

Step-by-step explanation:

The sum of the probabilities that cover all possibilities is 1 (the Law of Total Probability).

So P(white) + P(black) + P(red) = 1

=> P(red) = 1 - P(white) - P(black)

=> P(red) = 1 - 3/10 - 2/5

Putting over the common denominator of 10, this is

P(red) = 10/10 - 3/10 - 4/10 = 3 / 10.

For the next bit, we have

P(black) = ( # black balls ) / ( total # balls)

=> 2 / 5  =  20 / (total # balls)

=> total # balls = ( 20 x 5 ) / 2 = 10 x 5 = 50