question_answer

A bag contains 15 white and some black balls. If the probability of drawing a black ball from the bag is thrice that of drawing a white ball, find the number of black balls in the bag.

Answer:

Given, no. of white balls \[=15\]

Let                                no. of black balls \[=x\]

\[\therefore \]                            Total balls \[=15+x\]

According to the question,

P (Black ball) \[=3\times P\] (White ball)

\[\Rightarrow \]       \[\frac{x}{(15+x)}=3\times \frac{15}{(15+x)}\]

\[\Rightarrow \]               \[x=45\]

\[\therefore \]      No. of black balls in bag \[=45\]