Sana is three times as efficient as Hira. Together they complete a project in 12 days. How long would Hira take alone?
Correct answer: C. 48 days
If Hira does 1 unit a day, Sana does 3: together 4 a day, so the work is 4 × 12 = 48 units. Hira alone needs 48 ÷ 1 = 48 days.
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