Question
David alone can complete a work in 15 days and Rizwan
alone can do the same work in 30 days. David starts the work alone and on every alternate day, Rizwan joins him. In how many days will the work be completed?Solution
Given: David finishes work in 15 days → 1-day work = 1/15 Rizwan finishes in 30 days → 1-day work = 1/30 Work pattern: Day 1: David Day 2: David + Rizwan Repeats every 2 days 2-day work: Day 1: 1/15 Day 2: 1/15 + 1/30 = 1/10 Total in 2 days = 1/15 + 1/10 = (2 + 3)/30 = 5/30 = 1/6 So, every 2 days → 1/6 of work is done In 12 days: (12 ÷ 2) × 1/6 = 6 × 1/6 = 1 (full work) Therefore, 12 days is the answer
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