A bag contains 5 red, 8 white and 7 black balls. A ball is drawn at random from the bag. Find the probability that the drawn ball is red or white.

Given:

A bag contains 5 red, 8 white and 7 black balls. A ball is drawn at random from the bag. 

To do:

We have to find the probability that the ball drawn is red or white.

Solution:

Number of black balls $=7$

Number of red balls $=5$

Number of white balls $=8$

Total number of balls $=5+7+8=20$

This implies,

The total number of possible outcomes $n=20$.

Total number of favourable outcomes(drawing a red or white ball) $=5+8=13$.

We know that,

Probability of an event $=\frac{Number\ of\ favourable\ outcomes}{Total\ number\ of\ possible\ outcomes}$

Therefore,

Probability that the ball drawn is red or white $=\frac{13}{20}$

The probability that the ball drawn is red or white is $\frac{13}{20}$.