The average test score of a class was 61 marks. After five students who scored an average marks of 91 marks transferred out of the class, the average score of the remaining students became 51 marks. How many students were there in the class at first?
| |
(1) |
(2) |
| Number |
1 u |
1 u - 5 |
| Value |
61 |
51 |
| Total value |
61 u |
51 u - 255 |
Number of students at first = 1 u
Total score at first
= 1 u x 61
= 61 u
Total score of the 5 students
= 5 x 91
= 455
Total marks scored after 5 students transferred out
= 51 x (1 u - 5)
= 51 u - 255
61 u - 455 = 51 u - 255
61 u - 51 u = 455 - 255
10 u = 200
1 u = 200 ÷ 10 = 20
Number of students in the class at first
= 1 u
= 20
Answer(s): 20
