John can type a set of pages in 5 hours at a constant rate. If John types for 3 hours and Jack does the rest of the job, who works at 2/5 constant rate of John. How long will it take for Jack alone to do the rest of the job? Choose the correct choice from the following.
A) 1hrs  B) 3hrs  C) 4hrs  D) 5hrs  E) 7hrs
John will do 3/5 in 3 hrs, so John does 3/5 of the work ..   Therefore, Jack will do the remaining 2/5 th work alone..   As the speed of Jack is 2/5 rate of John, Jack will do the 2/5th work in same time that John takes to complete full job...   ans 5   5hrs
<result>D</result>
John can type a set of pages in 5 hours at a constant rate. If John types for 3 hours and Jack does the rest of the job, who works at 2/5 constant rate of John. How long will it take for Jack alone to do the rest of the job?