Question

Two tubes C and D can fill a reservoir in 18.75 minutes and 22.5 minutes respectively. Both the tubes are opened simultaneously.
After what time should the tube D be turned off to fill the reservoir completely in 15 minutes?

• A. 2.5 mins
• B. 4.5 mins
• C. 5.5 mins
• D. 7.5 mins
• E. 6.25 mins

Answer 1

The correct option is B

4.5 mins

Let D be turned off after 'x' minutes.

$\to$ part filled by (C + D) in 'x' min + part filled by C in (15 - x) min = 1

x($\frac{4}{75}$ +$\frac{2}{45}$) + (15 - x) $\frac{4}{75}$ = 1

$⟹$ 22x + 180 - 12x = 225

$\therefore$ x = 4.5