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 By: shirley wee (offline)  Sunday, April 07 2013 @ 07:03 AM CDT (Read 799 times)
shirley wee

Hi everybody! I'm stuck with this maths question. May you help me? Please show your working clearly.

Qn 1. In a Science test, the average marks of all the pupils in Class 6A was 86. After 4 pupils who scored an average of 71 marks left the class, the average marks of the remaining pupils became 88. How many pupils were there in Class 6A at first?

Chatty

Registered: 02/28/12
Posts: 68

 By: echeewh (offline)  Sunday, April 07 2013 @ 09:28 AM CDT
echeewh

Hey Shirley,

Following pls find my worked solution:

Let number of pupils in 6A be 1u.

Total marks = 86u
Marks of 4 pupils left = 4 × 71 = 284
Average marks of remaining pupils = (86u - 284) ÷ (u - 4)

Given average marks of remaining pupils is 88, we have ...

(86u - 284) ÷ (u - 4) = 88
86u - 284 = 88 × (u - 4)
86u - 284 = 88u - 352
88u - 86u = 352 - 284
2u = 68
u = 34

Hence, number of pupils in 6A = 34

==========

Trust this helps.

Kindly let me know again if this is different from your Answerkey or if theres further clarification.

Cheers,
Edward

Active Member

Registered: 04/21/11
Posts: 627

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