Pipe A can fill a pool in 12 hours at a constant rate. If Pipe A does the job for 8 hours and Pipe B does the rest of the job, which works at 1/3 constant rate of Pipe A. How long will it take for Pipe B alone to do the rest of the job?  Choose the correct choice from the following answers.
A) 12 hrs  B) 6 hrs  C) 8 hrs  D) 10 hrs  E) 24 hrs

Rationale: pipe a will do 8 / 12 in 8 hrs , so a does 2 / 3 of the work . . therefore , b will do the remaining 1 / 3 rd work alone . . as the speed of b is 1 / 3 rate of a , b will do the 1 / 3 rd work in same time that a takes to complete full job . . . ans 12 a
Answer: A