Question

A bag 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 black ball is 2/5 then find the probability of getting a red balls. If the bag contains 20 black balls then find the total number of balls in the bag​

Answer 1

let the number of red ball be 'x'

let the number of white balls be 'y'

number of black balls=20

therefore, total number of balls in a bag=x+y+20

i) p(white balls)=3/10=y/x+y+20

7y-3x=60. (a)

ii)p(black balls) = 2/5= 20/x+y+20

2x+2y=60. (b)

pair of linear equations are formed, I hope you will do that , after solving these equations you will get the value of x and y

THANKS

Answer 2

Let probability of black ball, red ball and white ball be P(B), P(R) and P(W) respectively.

According to question,

P(B) + P(R) + P(W) = 1

=> 2/5 + P(R) + 3/10 = 1

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

=> P(R) = 1 - 7/10 = 3/10

Now, P(B) = No. of black balls / Total balls

=> Total balls = No. black balls / P(B)

= 20 / (2/5)

= 50

Therefore, No. of White balls = Total balls x P(W) = 50 x 3/10 = 15 balls

And No. of Red balls = Total balls x P(R) = 50 x 3/10 = 15 balls