The average amount of money collected by a group of pupils at a flag day event was $107. When another 13 pupils turned up to help, the total amount donated increased by $779 and the average amount of money collected became $90. 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 |
107 |
90 |
Total Value |
107 u + 779 |
90 u + 1170 |
Number of pupils at first = 1 u
Total amount collected by the pupils at first
= 1 u x 107
= 107 u
Total amount collected by the pupils in the end
= 90 x (1 u + 13)
= 90 u + 1170
107 u + 779 = 90 u + 1170
107 u - 90 u = 1170 - 779
17 u = 391
1 u = 391 ÷ 17 = 23
Number of pupils at first
= 1 u
= 23
Answer(s): 23