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**

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Trust this helps.

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

Cheers,

Edward