The average mass of a group of girls was 35 kg. When a boy, Cody, joined the group, the average mass of the group became 32 kg. If Cody 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 |
32 |
Total value |
35 u |
32 u + 32 |
35 u + 20 = 32 u + 32
35 u - 32 u = 32 - 20
3 u = 12
1 u = 12 ÷ 3 = 4
Number of girls in the group in the end = 4
Answer(s): 4