The average test score of a class was 61 marks. After three pupils who scored an average marks of 97 marks transferred out of the class, the average score of the remaining pupils became 57 marks. How many pupils were there in the class in the end?
|
(1) |
(2) |
Number |
1 u |
1 u - 3 |
Value |
61 |
57 |
Total value |
61 u |
57 u - 171 |
Number of pupils at first = 1 u
Total score at first
= 1 u x 61
= 61 u
Total score of the 3 pupils
= 3 x 97
= 291
Total marks scored after 3 pupils transferred out
= 57 x (1 u - 3)
= 57 u - 171
61 u - 291 = 57 u - 171
61 u - 57 u = 291 - 171
4 u = 120
1 u = 120 ÷ 4 = 30
Number of pupils in the class in the end
= 1 u - 3
= 30 - 3
= 27
Answer(s): 27