Question

There are 30 cards numbered from 1 to 30. One card is drawn at random. Find the probability that the number on the selected card is not divisible by 3.

Answer 1

The possible outcomes are 1,2,3,4,................30.
Number of all possible outcomes = 30

Out of these, the numbers divisible by 3 are 3, 6, 9,12,15,18, 21, 24, 27 and 30.
Total numbers divisible by 3 = 10

Let E be the event of getting a number that is not divisible by 3.

Then, number of favourable outcomes = 30 − 10 = 20

∴ P (getting a number that is not divisible by 3) = P (E) = $\frac{20}{30}=\frac{2}{3}$