The average test score of a group of students was 79 marks. After two students who scored an average of 98 marks left the group, the average score of the group became 77 marks. How many students were there at first?
| |
At first |
Left |
In the end |
| Number |
1 u + 2 |
2 |
1 u |
| Value |
79 |
98 |
77 |
| Total value |
79 u + 158 |
196 |
77 u |
Number of students in the end = 1 u
Number of students at first = 1 u + 3
Total test score in the end
= 1 u x 77
= 77 u
Total test score at first
= 79(1 u + 2)
= 79 u + 158
Total test score for students who left
= 2 x 98
= 196
Total test score at first is equal to sum of the total score in the end and total score of the students who left.
79 u + 158 = 77 u + 196
79 u - 77 u = 196 - 158
2 u = 38
1 u = 38 ÷ 2 = 19
Number of students at first
= 1 u + 2
= 19 + 2
= 21
Answer(s): 21
