The average amount of money collected by a group of pupils at a flag day event was $100. When another 13 pupils turned up to help, the total amount donated increased by $625 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 + 13 |
| Value |
100 |
85 |
| Total Value |
100 u + 625 |
85 u + 1105 |
Number of pupils at first = 1 u
Total amount collected by the pupils at first
= 1 u x 100
= 100 u
Total amount collected by the pupils in the end
= 85 x (1 u + 13)
= 85 u + 1105
100 u + 625 = 85 u + 1105
100 u - 85 u = 1105 - 625
15 u = 480
1 u = 480 ÷ 15 = 32
Number of pupils at first
= 1 u
= 32
Answer(s): 32
