Question

All possible 3-digit numbers made with only the digits 1 and 2 are written on separate pieces of paper. Without looking, Liam takes one piece. What is the probability that the number on the paper will use just one digit?

Answer 1

To find the probability you need to know the number of desired outcomes (i.e. one digit only used) and the total number of outcomes.

In this case there are 3 desired outcomes - 111, 222, 333.

Since any of the 3 positions in the 3-digit number can be any of 3 numbers, there are 3 x 3 x 3 = 27 total possible outcomes.

The probability of having a desired outcome is 3 / 27 = 1 / 9 = 11.1%