Two persons A and B can complete a piece of work in 30 days and 60 days respectively. If they work together, what part of the work will be completed in 10 days?  Choose the correct choice from the following options:
A) 1 / 8
B) 1 / 3
C) 1 / 6
D) 1 / 2
E) 5 / 3

Rationale: a ' s one day ' s work = 1 / 30 b ' s one day ' s work = 1 / 60 ( a + b ) ' s one day ' s work = 1 / 30 + 1 / 60 = 1 / 20 the part of the work completed in 10 days = 10 ( 1 / 20 ) = 1 / 2 . answer : d
Answer: D