Some pupils took a Math exam. Their average score was 78.9 marks. One of the pupils' scores was wrongly recorded as 78 marks instead of 87 marks. As a result, the average score was calculated as 78.4 marks. How many pupils sat for the exam?
|
If that pupil's score was 87 |
If that pupil's score was 78 |
Number of pupils |
1 u |
1 u |
Average score |
78.9 |
78.4 |
Total score |
78.9 u |
78.4 u |
Difference in the scores due to being wrongly recorded
= 87 - 78
= 9
Difference in total scores of the pupils is due to the difference in the wrongly recorded score.
78.9 u - 78.4 u = 9
0.5 u = 9
1 u = 9 ÷ 0.5 = 18
Number of pupils = 18
Answer(s): 18