Question

An urn contains 9 red balls and x green balls. If the probability of picking a red ball is thrice that of picking a green ball, then x = ________.

Answer 1

An urn contains 9 red balls and x green balls. If the probability of picking a red ball is thrice that of picking a green ball, then x = __3__.


Explanation

Total number of balls = x + 9

Probability of picking a red ball = $\frac{9}{x+9}$

Probability of picking a green ball = $\frac{x}{x+9}$

It is given that,

Probability of picking a red ball = 3 × Probability of picking a green ball

$$\begin{gathered} \Rightarrow \frac{9}{x+9}=3\times \frac{x}{x+9} \\ \Rightarrow 3x=9 \\ \Rightarrow x=3 \end{gathered}$$