Question

A bag contains $5$ red balls and some blue balls. If the probability of drawing a blue ball is double to that of a red ball, find the number of blue balls in the bag.

• A. $10$
• B. $5$
• C. $15$
• D. $20$

Answer 1

Answer: (A)

$10$

let the number of blue balls is $x$.

Total number of balls id $(x+5)$

the probability of drawing a blue ball is $\frac{x}{x+5}$

the probability of drawing a red ball is $\frac{5}{x+5}$

$\frac{x}{x+5}=2\times \frac{5}{x+5}$ (probability of drawing blue ball is double to that of red ball)

$x=10$

$\therefore$ the number of blue balls$=10$