The average amount of money collected by a group of pupils at a flag day event was $108. When another 15 pupils turned up to help, the total amount donated increased by $608 and the average amount of money collected became $85. How many pupils were there in the group at first?
| |
Number of pupils
at first |
Number of pupils
in the end |
| Number |
1 u |
1 u + 15 |
| Value |
108 |
85 |
| Total Value |
108 u + 608 |
85 u + 1275 |
Number of pupils at first = 1 u
Total amount collected by the pupils at first
= 1 u x 108
= 108 u
Total amount collected by the pupils in the end
= 85 x (1 u + 15)
= 85 u + 1275
108 u + 608 = 85 u + 1275
108 u - 85 u = 1275 - 608
23 u = 667
1 u = 667 ÷ 23 = 29
Number of pupils at first
= 1 u
= 29
Answer(s): 29
