arithmetic - watson can do a certain work in the same time in which steven and james together can do it if watson and steven together could do it in 15 days and james alone in 30 days then steven alone could do it in - skillgun

Solution: Let A = Watson, B = Steven, C = James.
(A+B)'s 1 day;s work = 1/15; C's 1 day's work = 1/30.
(A+B+C)'s 1 day;s work = (1/15 + 1/30) = 3/30 = 1/10. ----> (1)
also, A's 1 day's work = (B+C)'s 1 day's work ----> (2)
from (1) and (2), we get : 2*(A's 1 day's work) = 1/10.
A's 1 day's work = 1/20.
.'. B's 1 day's work = (1/15 - 1/20) = 1/60.
so, Steven alone can could do the work in 60 days.