Given:
P can do a piece of work = 20 days
Q can do a piece of work = 40 days
P leaves that work 10 days before completion
Concept used:
Total work = LCM
Formula used:
Efficiency = Work/Time
Calculations:
Total work = LCM = 40
Person
Time
Total work
Efficiency
P
20 days
40
40/20 = 2
Q
40 days
40/40 = 1
Let the work finishes in x days
So, Time in which P works = (x – 10)
Work done by P in (x – 10) days = 2 × (x – 10)
Work done by Q in x days = 1 × x = x
Now,
⇒ 2(x – 10) + x = 40
⇒ 2x – 20 + x = 40
⇒ 3x = 60
⇒ x = 20 days
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