Machine A takes 50 hours to complete a certain job and starts that job at 6AM. After four hour of working alone, machine A is joined by machine B and together they complete the job at 1PM. How long would it have taken machine B to complete the job if it had worked alone for the entire job? Choose the correct choice from the following answers: A) 9 B) 88.88 C) 4.88 D) 2.88 E) 3.88
Let us assume total job = 100 units   A finishes 100 units in 50 hrs(given)   Hence A (working rate)= 2 units /hr   Now Given that A works for 4 hr( so 8 units done) then A and B finish total work in 7 hours. Hence A and B finish 92 units in 3 hours. Of these 3x2=6 units were done by A. Hence B did 86 units in 3 hours.   Hence B(working rate)= 86/3 units /hr   Hence B takes 100x3/86 = 3.88 hours to complete the job.   Answer 3.88.
<result>E</result>
Machine A takes 50 hours to complete a certain job and starts that job at 6AM. After four hour of working alone, machine A is joined by machine B and together they complete the job at 1PM. How long would it have taken machine B to complete the job if it had worked alone for the entire job?