- A85.6
- B82.2
- C78.4
- D80.9
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Concept: Combined average = (sum of n × average) ÷ total students.
- Totals: 2400 (30 × 80), 3375 (45 × 75), 4500 (50 × 90) → sum 10275.
- Students = 30 + 45 + 50 = 125.
- Average = 10275 ÷ 125 = 82.2.
Trick: Take 80 as base: deviations = 45 × (−5) + 50 × (+10) = −225 + 500 = 275; 275 ÷ 125 = 2.2 → 80 + 2.2 = 82.2.
Answer: (B) 82.2
अवधारणा: संयुक्त औसत = (संख्या × औसत का योग) ÷ कुल छात्र।
- कुल अंक: 2400 (30 × 80), 3375 (45 × 75), 4500 (50 × 90) → योग 10275।
- छात्र = 30 + 45 + 50 = 125।
- औसत = 10275 ÷ 125 = 82.2।
ट्रिक: 80 को आधार मानें: विचलन = 45 × (−5) + 50 × (+10) = 275; 275 ÷ 125 = 2.2 → 82.2।
उत्तर: (B) 82.2
