Ram completes 60% of a task in 15 days and then takes the help of Rahim and Rachel. Rahim is 50% as efficient as Ram is and Rachel is 50% as efficient as Rahim is. In how many more days will they complete the work?

Let the total work be 25x units

Ram completes 60% of the task in 15 days.

Ram's efficiency = x units per day

Rahim is 50% as efficient as Ram is and Rachel is 50% as efficient as Rahim is

Efficiency of Rahim = 0.5x units per day

Efficiency of Rahim = 0.25x units per day

Ram will come 15x units in 15 days.

The remaining 10x units of work will be done by Ram, Rahim, Rachel.

=$$\ \frac{10x}{x+0.5x+0.25x}$$

= $$\ \frac{10}{1.75}$$

=$$\ \frac{1000}{175}$$

=$$\frac{40}{7}$$

C is the correct answer.