The average of a set of data is equal to the sum of the values divided by the number of data present. So, if we have three numbers, the average would be:
let x, y and z represent the three numbers
average = x + y + z / 3 = 45
Two number are equal in value, so let x = y. Substituting the value to the expression of average,
45 = x + x + z / 3
45 = 2x + z / 3
It said that the last number is 89 so z is equal to 89.
45 = 2x + 89 / 3
135 = 2x + 89
46 = 2x
x = 23
Therefore, the two numbers are both 23.
