Ram, Ravi and Reena can do a piece of work in 16, 20 and 24 days, respectively. They began the work together but Ravi left the work 5 days before the completion of the work. In how much time did they finish the work together?

Correct option is C

Given:
Ram can complete the work in 16 days.
Ravi can complete the work in 20 days.
Reena can complete the work in 24 days.
Ravi leaves the work 5 days before completion.
Solution:
Total Work = LCM of 16, 20, and 24 is 240 unit
​$$\text{Ram's efficiency} = \frac{240}{16} = 15 \\\ \\\text{Ravi's efficiency} = \frac{240}{20} = 12 \\\ \\\text{Reena's efficiency} = \frac{240}{24} = 10$$
Work done by Ravi in last 5 Days = 12$$\times 5 = 60 unit$$ 
So, if this work also completed by Ravi.
Then Total Work = 240 + 60 = 300 unit
Time taken by three of them to complete the work = $$\frac{300}{37}= 8.10\, \text{days} \approx 8 \, \text{days}$$​​