In a test,the average class score was 77 marks.Mr Wong discovered that he had recorded 14 students’ marks wrongly.After adding 3 marks to each of these students,the average class score became 79.How many students were there in the class?
How to tackle this question?
sushi88
Let u be the number of students.
Total marks = 77u, Added marks to 14 students = 14 x 3 = 42
(77u + 42) / u = 79 [Average = Total marks/Total students]
77u + 42 = 79u
2u = 42 => u =21
Hence there were 21 students in the class.
mr.tan
No algebra solution He added a total of 14 x 3 = 42 marks. That 42 is spread equally across all students, increasing the average score by 79 - 77 = 2. So there are 42 / 2 = 21 students. Algebra solution Let there be u students. Total score is 77u initially. After correcting, total score is 77u + 14 x 3 = 77u + 42. But average becomes 79, so 79u = 77u + 42. That means 2u = 42 and u = 21. So there are 21 students.
