The average mass of a group of girls was 36 kg. When a boy, Zane, joined the group, the average mass of the group became 32 kg. If Zane 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 |
32 |
Total value |
36 u |
32 u + 32 |
36 u + 20 = 32 u + 32
36 u - 32 u = 32 - 20
4 u = 12
1 u = 12 ÷ 4 = 3
Number of girls in the group in the end = 3
Answer(s): 3