A bag contain 5 red balls and some blue balls. If the probability of drawing a blue ball from the bag is thrice that of a red ball, find the number of blue balls in the bag.

Question

Philoid · Accepted Answer

Let the no. of blue balls in the bag be x.

Let B and R be the event of drawing a blue and red ball respectively.

∴ total no. of balls in the bag = x + 5

According to question –

Probability of drawing blue ball

= 3 × Probability of drawing blue ball

⇒ [no. of blue balls/total no. of balls]

= 3 × [no. of red balls/total no. of balls]

⇒ (x/x + 5) =3 × (5/x + 5)

∴ x = 15

Thus, the no. of blue balls in the bag is 15.