Manish can complete a work in 21 days and Karan can complete the same work in 28 days. If both together work for 7 days, then what fraction of total work is left?
Let total work to be done = L.C.M. (21,28) = 84
Manish can complete the work in 21 days, => Manish's efficiency = $$\frac{84}{21}=4$$ units/day
Similarly, Karan's efficiency = $$\frac{84}{28}=3$$ units/day
Now, (Manish+Karan)'s 7 day's work = $$(4+3)7=49$$ units
Fraction of work that is left = $$\frac{(84-49)}{84}=\frac{35}{84}=\frac{5}{12}$$
=> Ans - (D)
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