A and B together can complete a work in 12 days. A alone can complete it in 20 days. If B does the work only for half a day daily, then in how many days A and B together will complete the work?	Options.
A) 10 days
B) 11 days
C) 15 days
D) 20 days
E) none of these

Rationale: b ' s 1 day ' s work = ( 1 / 12 - 1 / 20 ) = 2 / 60 = 1 / 30 now , ( a + b ) ' s 1 day ' s work = ( 1 / 20 + 1 / 60 ) = 4 / 60 = 1 / 15 so , a and b together will complete the work in 15 days . correct option : c
Answer: C