P and Q together can complete a work in 20 days. If P alone can complete the same work in 36 days, then in how many days Q alone can complete the same work?
Let the total work be 180 units (LCM of 20 and 36)
Efficiency of P+Q = 180/20 = 9 units per day
Efficiency of P = 180/36 = 5 units per day
Then, Efficiency of Q = 9-5 = 4 units per day
Therefore, Q can do the work together in 180/4 = 45 days
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