B completes a work in 3 days. A alone can do it in 10 days. If both work together, the work can be completed in how many days? Choose the most appropriate option
A) 2.31 days  B) 4.31 days  C) 5.31 days  D) 6.31 days  E) 7.31 days

Rationale: 1 / 3 + 1 / 10 = 13 / 30 30 / 13 = 2.31 days answer : a
Answer: A