Question

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

Answer 1

let Blu ball is. x
total Ball is 5+x
probability of red ball 5/(5+x)
probability of blue balls is x/(5+x)
according to question x/(5+x)=(5×2)/(5+x)
or, x/(5+x)=10/(5+x)
or, x= 10
this is your answer

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