Pipe 1 can empty a tank in 6 h while pipe 2 can do so in 18 h. If both are working together, in how much time will they empty the full tank?

Correct option is D

Given:

Pipe 1 can empty the tank in 6 hours

Pipe 2 can empty the tank in 18 hours

Formula Used:

Combined rate = $$\left( \frac{1}{T_1} + \frac{1}{T_2} \right)$$​​

Time = $$\frac{1}{\text{Combined rate}}$$​

Solution:

Combined rate =$$\frac{1}{6} + \frac{1}{18} = \frac{3 + 1}{18} = \frac{4}{18} = \frac{2}{9}$$​

Time =$$\frac{1}{\frac29} = \frac{9}{2} = 4.5 \, \text{hours}$$

Alternate Method:

Time = $$\frac{18}{4}= 4.5$$ hours​