30 men can do a work in 40 days. When should 20 men leave the work so that the entire work is completed in 40 days after they leave the work? Choose the correct choice from the following answers.
A) 22 days  B) 10 days  C) 77 days  D) 88 days  E) 55 days

Rationale: "total work to be done = 30 * 40 = 1200 let 20 men leave the work after ' p ' days , so that the remaining work is completed in 40 days after they leave the work . 40 p + ( 20 * 40 ) = 1200 40 p = 400 = > p = 10 days answer : b"
Answer: B