Question

A bag contains $10$ white balls and $X$ black balls. If probability of drawing white balls is double that black ball then answer the following: Find the value of $X$.

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

Answer 1

The correct option is C $20$

Total no. of balls $=10+X$

Probability of drawing black ball $=\frac{X}{10+X}$

Probability of drawing white ball $=\frac{10}{10+X}$

Given that the probability of drawing white balls is double that of black ball

$\therefore \frac{X}{10+X}=2\left(\frac{10}{10+X}\right)$

$\therefore \frac{X}{10+X}=\left(\frac{20}{10+X}\right)$

$\therefore X=20$