A and B together can do a piece of work in 20 days. B and C together can do the same of work in 25 days. C and A together can do the same work in 15 days. In how many days A alone can do the same work?

A/c to question ,

$$\frac{1}{A} + \frac{1}{B} =\frac{1}{20}$$

$$\frac{1}{B} + \frac{1}{C} =\frac{1}{25}$$

$$\frac{1}{C} + \frac{1}{A} =\frac{1}{15}$$

Adding these equations ,

2($$\frac{1}{A} + \frac{1}{B} +\frac{1}{C}$$) = ($$\frac{1}{20} + \frac{1}{25} +\frac{1}{15}$$)

$$\frac{1}{A} + \frac{1}{B} +\frac{1}{C} = \frac{47}{600}$$

$$\frac{1}{A} = \frac{47}{600} - \frac{1}{25} = \frac{23}{600}$$

So, the answer would be option a)$$\frac{600}{23}$$