A can do a piece of work in 40 days; B can do the same in 20 days. A started alone but left the work after 10 days, then B worked at it for 10 days. C finished the remaining work in 10 days. C alone can do the whole work in?  Select the correct option:  A) 24 days  B) 60 days  C) 86 days  D) 40 days  E) 17 days
10/40 + 10/20 + 10/x = 1   x = 40 days   Answer:40 days
<result>D</result>
A can do a piece of work in 40 days; B can do the same in 20 days. A started alone but left the work after 10 days, then B worked at it for 10 days. C finished the remaining work in 10 days. C alone can do the whole work in?