Question

A lock has 5 buttons. The lock is opened by pushing two buttons simultaneously and then by pushing one button alone. How many combinations are possible?

Answer 1

We first must calculate how many ways 2 oblects can be chosen from 5.

combinations = 5! / 2! * (5-2)!

combinations = 5*4 / 2

combinations = 10

There are 10 ways to choose the 2 buttons and 5 ways to choose the final butto so there are 10 * 5 = 50 different ways.

Source

1728.com/combinat.htm