In a group of five friends, the sums of the ages of each group of four of them are 124, 128, 130, 136, and 142. What is the age of the youngest?
23
[142 - 136] / 4 + [142 - 130] /4 + [142 - 128] / 4 + [142 - 124] / 4 =1.5 + 3 + 3.5 + 4.5 = 12.5 years difference between the average of oldest and the youngest.
142 / 4 =35.5 years the average of the oldest 4
35.5 - 12.5 = 23 years - the youngest.
