Question

Choose a natural number between 1 and 100 inclusive. What is the probability that the number chosen is not a multiple of 5 (enter the probability as a fraction)

Answer 1

We will solve as follows:

First: We determine the number of multiples of 5 between 1 and 100:

$100=5n\Rightarrow n=20$

So, there are 20 multiples of 5 between 1 and 100 [Inclusive].

Second: We determine the probability of not chosing a multiple of 5:

$p=\frac{80}{100}\Rightarrow p=\frac{4}{5}$

So, the probabilty is 4/5 that the number chosen at random will not be a multiple of 5.