A and B can together complete a task in 21 days. If A alone takes 42 days to complete the task, then the number of days that B would take to do the task alone is:
A and B can together complete a task in 21 days. If A alone takes 42 days to complete the task.
LCM of 21 and 42 is 42 which is total work.
The efficiency of A =Â $$\frac{42}{42}$$ = 1 unit/day
The efficiency of A and B together = $$\frac{42}{21}$$ = 2 units/day
The efficiency of B = 2-1 = 1Â unit/day
The number of days taken by B to do the task alone =Â $$\frac{42}{1}$$
=Â 42 days
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