The average mass of a group of girls was 36 kg. When a boy, Andy, joined the group, the average mass of the group became 34 kg. If Andy 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 |
36 |
34 |
Total value |
36 u |
34 u + 34 |
36 u + 20 = 34 u + 34
36 u - 34 u = 34 - 20
2 u = 14
1 u = 14 ÷ 2 = 7
Number of girls in the group in the end = 7
Answer(s): 7