A student scored an average of 78 marks in 4 subjects. If his average in all 5…
2025
A student scored an average of 78 marks in 4 subjects. If his average in all 5 subjects is 80, what are the marks he scored in the 5th subject?
Answer: B. 88 — Concept: For any group of values, Total = Average × Number of items. When a new item joins the group, that item's own value equals the New Total (after…
- A.
90
- B.
88
- C.
86
- D.
84
Attempted by 12 students.
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Correct answer: B
Concept: For any group of values, Total = Average × Number of items. When a new item joins the group, that item's own value equals the New Total (after joining) minus the Old Total (before joining).
Total marks in the first 4 subjects = Average × Count = 78 × 4 = 312.
Total marks in all 5 subjects = New average × Count = 80 × 5 = 400.
Marks scored in the 5th subject = New total − Old total = 400 − 312 = 88.
Cross-check: Adding 88 to the original total of 312 gives 400, and 400 ÷ 5 = 80, which matches the given average of 5 subjects — confirming 88 is correct.