Answer:
A simple event is an event where all the outcomes are equally likely.
Suppose a dice, where you have 6 possible numbers, this will be a simple event if the probability to getting a given number is equal to the number of times that the given number is in the dice (1) divided by the total number of options:
p = 1/6
Here we have 8 circuits, and N is the number of defective ones.
Then the simple event can be written as:
P = N/8
this gives use the probability of selecting at random a defective circuit board.
Then the only simple event here is selecting circuit board, that can be defective or not (probability of selecting at random a defective one p = N/8, probability of selecting at random a non-defective one P = 1 - N/8)