The average mass of a group of girls was 35 kg. When a boy, Howard, joined the group, the average mass of the group became 30 kg. If Howard had a mass of 20 kg, how many girls were there in the group in the end?
|
At first |
In the end |
Number |
1 u |
1 u + 1 |
Value |
35 |
30 |
Total value |
35 u |
30 u + 30 |
35 u + 20 = 30 u + 30
35 u - 30 u = 30 - 20
5 u = 10
1 u = 10 ÷ 5 = 2
Number of girls in the group in the end = 2
Answer(s): 2