Question

A bag contains 5 red balls and some Blue Balls.if the probability of drawing a blue ball is double the probability of drawing a red ball, determine the number of blue balls in the bag.

Answer 1

let the blue balls=x
total outcome= 5+x
p(R)=5/5+x
p(B)=x/5+x
x/5+x=2(5/5+x)
x=10

Answer 2

Solution :

Let there be x blue balls in the bag.

∴ Total number of balls in the bag = 5 + x

Now,

          $p_{1}$ = Probability of drawning a blue ball = $\frac{x}{5 + x}$

          $p_{2}$ = Probability of drawing a red ball = $\frac{5}{5 + x}$

But it is given that $p_{1}$ = $2p_{2}$

⇒ $\frac{x}{5 + x}$ = $2 \times \frac{5}{5 + x}$

⇒ x = 10