A box contains 500 bulbs of which 100 are defective. What is the probability of receiving a defective bulb when a bulb is picked from the box randomly??

The probability of an event is given as:

Probability of an event = $\frac{\mathrm{Outcomes} \mathrm{of} \mathrm{an} \mathrm{event}}{\mathrm{Total} \mathrm{possible} \mathrm{outcomes}}$

There is a total of 500 bulbs of which 100 are defective.

Probability of getting a defective bulb =$\frac{ \mathrm{Number} \mathrm{of} \mathrm{defective} \mathrm{bulbs}}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{bulbs}}$

$\begin{array}{rcl} & =& \frac{100}{500}=\frac{1}{5}\end{array}$

Therefore,$\frac{1}{5}$ is the correct response.