Question

A bag contains, white, black and red balls only. A ball is drawn at random from the bag. If the probabilityof getting a white ball is and that of a black ball is , then find the probability of getting a red ball. If thebag contains 20 black balls, then find the total number of balls in the bag​

Answer 1

BONJOUR MATE!!

Let the no of white balls be = x

Let the no of red balls be = y

number of balls black balls =20

total number of balls =x+y+20

Probability of getting a white ball =3/10

x/x+y+20=3/10

=> 10x=3x+3y+60

=> 7x−3y=60------(1)

Probability of getting a blind ball =2/5

(i.e)20x+y+20=25

= 100=2x+2y+40

=> 2x+2y=60

or x=y=30 ----------(2)

Solving (1) and (2) we get,

7x−3y=60

x+y=30

______________

7x−3y=60

7x+7y=210

________________

−10y=150

=> y=15

x=15

Answer : 15