A bag contains 20 white shirts and 10 red shirt. One shirt is drawn out of the bag. What is the probability that it is: a) A white shirt. b)A red shirt?

There are 20 white shirts and 10 red shirts.

$$\text{Total number of shirts} = 20 + 10 = 30$$

The number of white shirts is 20.

$$P(\text{white shirt}) = \frac{\text{Number of white shirts}}{\text{Total number of shirts}} = \frac{20}{30} = \frac{2}{3}$$

The probability of drawing a white shirt is $\boxed{\frac{2}{3}}$.

The number of red shirts is 10.

$$P(\text{red shirt}) = \frac{\text{Number of red shirts}}{\text{Total number of shirts}} = \frac{10}{30} = \frac{1}{3}$$

The probability of drawing a red shirt is $\boxed{\frac{1}{3}}$.