If 12 men or 20 women can do a work in 54 days, then in how many days can 9 men and 12 women together do the work?
12 men or 20 women can do a work in 54 days
=> $$12m=20w=\frac{1}{54}$$
=> $$9m=\frac{1}{72}$$ and $$12w=\frac{1}{90}$$
Thus, 9 men and 12 women together do the work in = $$1\div(\frac{1}{72}+\frac{1}{90})$$
= $$1\div(\frac{5+4}{360})=\frac{360}{9}=40$$ days
=> Ans - (C)
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