Question

A bag contains white black red balls only A ball is drawn at random from the bag If the probability of getting a white ball is 3/10 and that of a black ball is 2/5 then find the probability of getting a red ball .If the bag contain 20 black balls then find the total number of balls

Answer 1

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=x+y+20

Probability of getting a white ball =310=310

xx+y+20=310xx+y+20=310

=> 10x=3x+3y+6010x=3x+3y+60

=> 7x−3y=607x−3y=60------(1)

Probability of getting a blind ball =25=25

(i.e)20x+y+20=2520x+y+20=25

= 100=2x+2y+40100=2x+2y+40

=> 2x+2y=602x+2y=60

or x=y=30x=y=30 ----------(2)

Solving (1) and (2) we get,

7x−3y=607x−3y=60

x+y=30x+y=30

______________

7x−3y=607x−3y=60

7x+7y=2107x+7y=210

________________

−10y=150−10y=150

=> y=15y=15

x=15x=15

Answer : 15

Answer 2

Answer:

Pr(Red ball)=1-3/10-2/5=3/10

Total number of balls * 2/5=20 black balls

∴Total number of balls =5/2*20=50

Hope this helps :)

Step-by-step explanation: