The average test score of a class was 70 marks. After five pupils who scored an average marks of 97 marks transferred out of the class, the average score of the remaining pupils became 61 marks. How many pupils were there in the class at first?
|
(1) |
(2) |
Number |
1 u |
1 u - 5 |
Value |
70 |
61 |
Total value |
70 u |
61 u - 305 |
Number of pupils at first = 1 u
Total score at first
= 1 u x 70
= 70 u
Total score of the 5 pupils
= 5 x 97
= 485
Total marks scored after 5 pupils transferred out
= 61 x (1 u - 5)
= 61 u - 305
70 u - 485 = 61 u - 305
70 u - 61 u = 485 - 305
9 u = 180
1 u = 180 ÷ 9 = 20
Number of pupils in the class at first
= 1 u
= 20
Answer(s): 20