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ATQ, we can say that Efficiency of X = ‘e’ unit/day 10 × (40 + 30) + 4 × (28 + ‘e’) = 840 10 × 70 + 4(28 + ‘e’) = 840 4(28 + ‘e’) = 840 – 700 4(28 + ‘e’) = 140 28 + ‘e’ = 140/4 28 + ‘e’ = 35 ‘e’ = 35 – 28 ‘e’ = 7 unit/days X alone complete the work in  = 840/7 = 120 Days
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