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Question

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?

Answer

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.

0 Replies 1 Like
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.

0 Replies 1 Like
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