The average amount of money collected by a group of students at a flag day event was $100. When another 11 students turned up to help, the total amount donated increased by $720 and the average amount of money collected became $81. How many students were there in the group in the end?
|
Number of students at first |
Number of students in the end |
Number |
1 u |
1 u + 11 |
Value |
100 |
81 |
Total Value |
100 u + 720 |
81 u + 891 |
Number of students at first = 1 u
Total amount collected by the students at first
= 1 u x 100
= 100 u
Total amount collected by the students in the end
= 81 x (1 u + 11)
= 81 u + 891
100 u + 720 = 81 u + 891
100 u - 81 u = 891 - 720
19 u = 171
1 u = 171 ÷ 19 = 9
Number of students in the end
= 1 u + 11
= 9 + 11
= 20
Answer(s): 20