Question

A bag contains white,black and red balls only.A ball is drawn at random from the bag.If the probability of getting a white ball is $\frac{3}{10}$ and that of a black ball is $\frac{2}{5}$,then find thew probability of getting a red ball.if the ball bag contains 20 black balls,then find the total number of balls in the bag.

Answer 1

Given,the probability of getting a white ball

$\Rightarrow P\left(W\right)=\frac{3}{10}$

and the probability of getting a black ball

$\Rightarrow P\left(B\right)=\frac{2}{5}$

then,the probability of getting a red ball

$\Rightarrow P\left(R\right)=1-\frac{3}{10}-\frac{2}{5}=\frac{10-3-4}{10}=\frac{3}{10}$

Now, $\frac{2}{5}$ of total number of balls=20

Total number of balls=$\frac{20\times 5}{2}$

=50
Hence,the total no.of balls in the bag is 50.