Amar is 2 times as good a workman as Badal and therefore is able to finish a job in 15 days less than Badal. In how many days can they together complete the job?

Ratio of times taken by Amar and Badal = 1 : 2

The time difference is (2 - 1) 1 day while Badal take 2 days and Amar takes 1 day.

If difference of time is 1 days, Badal takes 2 days.

If difference of time is 15 days, Badal takes = $$\frac{2}{1} \times 15 = 30$$ days

So, Amar takes 30 days

Amar's 1 day's work = $$\frac{1}{15}$$

Badal's 1 day's work = $$\frac{1}{30}$$

(Amar + Badal)'s 1 day's work together = $$\frac{1}{30} + \frac{1}{15} = \frac{3}{30} = \frac{1}{10}$$

$$\therefore$$ Amar and Badal together can do the work in = 10 days

=> Ans - (C)