Question

A building has 20 floors above the ground floor. Four people walk into this building on the ground floor, on their way to some floor above the ground.

When they reach the elevator, each person only presses the button of the floor they are going to.

What is the probability that 4 buttons for consecutive floors are pressed?

Answer 1

1/24

Explanation:

using Permutations and Combinations

Answer 2

1/24

Explanation:

This is a mutually exclusive event.

There are four possible floors and four people.

The probability that the first floor is selected is 1/4

The same probability exists for the second floor and the third and the fourth.

So, the probability of all four people choosing different floors is 1/4 * 1/4 * 1/4 * 1/4 = 1/24