If A can complete the work in x days, b can complete the same piece of work in y days and c can complete the same work in z days. In how many days that they can complete the work simultaneously?	Select.
A) cannot be determined  B) xyz/(x+y+z)  C) xyz  D) x+y+z  E) (x+y+z)/xyz
A's one day work=1/x..similarly b and c's one day work is 1/y and 1/z respectively.   a+b+c=(1/x)+(1/y)+(1/z)=(x+y+z)/xyz(one day work)   Total working days=xyz/(x+y+z).   The option xyz/(x+y+z) is the answer.
<result>B</result>
If A can complete the work in x days, b can complete the same piece of work in y days and c can complete the same work in z days. In how many days that they can complete the work simultaneously?