I don't know what you think the chain rule is but here is a solution.Originally Posted by joshirabi
A does 1/30 of the work per day, B does 1/40 and C 1/60.
Total work done by B is 10/40=1/4. Total work done by A is 14/30=7/15.
So total work done by A and B is 1/4+7/15=43/60, leaving 17/60 of the
work to be done by C. However C does 1/60 of the work per day, hence
works for a total of 17 days.