Question

A bag contains 8 white balls and some yellow balls. if the probability of drawing a white ball is twice of a yellow ball, then then number of yellow balls in the bag is?

Answer 1

Let there be X yellow balls in the bag

Total number of balls in the bag= 8+x

P1(yellow)= probability of drawing a yellow ball= x/(8+x)

P2(white)= probability of drawing a white ball= 8/(8+x)

P2=2P1 (given)

8/(8+x) = 2(x/(8+x))


8/(8+x) = 2x/8+x

8= 2x

x= 8/2= 4

Hence, the number of yellow balls in the bag are 4


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Hope this will help you....

Answer 2

Solution :-

Let the number of yellow balls be x

Number of white balls = 8

Total number of balls = 8 + x

Probability of picking a white ball, P(W) = 8/(8 + x)

Probability of picking a yellow ball, P(Y) = x/(8 + x)

Given = P(W) = 2*P(Y)

⇒ 8/(8 + x) = 2*x/(8 + x)

⇒ 64 + 8x = 16x + 2x²

⇒ 2x² + 16x - 8x - 64 = 0

⇒ (2x² + 8x - 64 = 0) ÷ 2 

= x² + 4x - 32 = 0

⇒ x² + 8x - 4x - 32 = 0

⇒ x(x + 8) - 4(x + 8) = 0

⇒ (x - 4) = 0 or (x + 8) = 0

⇒ x = - 8 is not possible.

So, x = 4

So, the number of yellow balls in the bag is 4.

Answer.