A can do a work in 3 days. B can do the same work in 6 days. If both A & B are working together in how many days they will finish the work?
Choose one:
A) 3
B) 5
C) 4
D) 2
E) 6

Rationale: "a rate = 1 / 3 b rate = 1 / 6 ( a + b ) rate = ( 1 / 3 ) + ( 1 / 6 ) = 1 / 2 a & b finish the work in 2 days correct option is d"
Answer: D