A and B working together can do a work in 10 days. If A can do the work in 15 days, then how many days will B take to do the same work?

30

A and B working together can do a work in 10 days

A and B one day work = 1/10

A can do the work in 15 days

A's alone one day work = 1/15

Assume B takes T days to complete the work alone

B's one day work = 1/T

Thus, 1/10 = 1/15 + 1/T

1/T = 1/10 - 1/15 = (3-2)/30

T = 30 days

The correct answer is Option (2) → 30