Two valves A and B can fill a sump in $$37\frac{1}{2}$$ minutes and 45 minutes respectively. Both valves are opened. The sump will be filled in just 30 minutes, if valve B is turned off after:
Let's Solve with LCM method.
LCM of ( $$\frac{75}{2}$$ and 45) = 225, assume this is total unit of work.
Thus, efficiency of A = $$\frac{225}{75/2}$$= 6 units/min and B = $$\frac{225}{45}$$ = 5 units/min.
Since A works for 30 mins, he will finish = 6 x 30 = 180 units.
Remaining Work = 225 - 180Â
= 45 units to be completed by B in = $$\frac{45}{5}$$ = 9 mins.
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