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.
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