A pipe can fill a tank in 18 hours. In how much time (in hours) will another pipe operating at one-third the efficiency of the first pipe fill a tank whose capacity is 50% of that of the first tank?

Let's assume the capacity of the first tank is 54 units.

A pipe can fill a tank in 18 hours.

Efficiency of first pipe = $$\frac{54}{18}$$ = 3 units/hour

Another pipe operating at one-third the efficiency of the first pipe fills a tank whose capacity is 50% of that of the first tank.

Efficiency of another pipe = $$\frac{1}{3}\times\ 3$$ = 1 unit/hour

The capacity of another tank = 50% of 54

= $$\frac{1}{2}\times54$$

= 27 units

Time taken by another pipe to fill that another tank = $$\frac{27}{1}$$

= 27 hours