The average exam score of a group of students was 65 marks. After 5 students who scored an average of 77 marks joined the group, the average score of all the students became 69 marks. How many students were there in the group at first?
| |
At first |
Joined |
In the end |
| Number |
1 u |
5 |
1 u + 5 |
| Value |
65 |
77 |
69 |
| Total value |
65 u |
385 |
69 u + 345 |
Number of students at first = 1 u
Number of students in the end = 1 u + 5
Total exam score at first
= 1 u x 65
= 65 u
Total exam score for students who joined
= 5 x 77
= 385
Total exam score in the end
= 69(1 u + 5)
= 69 u + 345
Total exam score in the end is equal to sum of the total score at first and total score of the students who joined.
69 u + 345 = 65 u + 385
69 u - 65 u = 385 - 345
4 u = 40
1 u = 40 ÷ 4 = 10
Number of students at first
= 1 u
= 10
Answer(s): 10
