Machine A takes 100 hours to complete a certain job and starts that job at 6AM. After ten hour of working alone, machine A is joined by machine B and together they complete the job at 6PM. How long would it have taken machine B to complete the job if it had worked alone for the entire job? Choose the correct answer
A) 24.65
B) 22.27
C) 2.273
D) 11.62
E) 21.13
Let us assume total job = 100 units   A finishes 100 units in 100 hrs(given)   Hence A (working rate)= 1 units /hr   Now Given that A works for 10 hr( so 10 units done) then A and B finish total work in 12 hours. Hence A and B finish 90 units in 2 hours. Of these 1x2=2 units were done by A. Hence B did 88units in 2 hours.   Hence B(working rate)= 44 units /hr   Hence B takes 100/44 = 2.273 hours to complete the job.   Answer 2.273.
<result>C</result>
Machine A takes 100 hours to complete a certain job and starts that job at 6AM. After ten hour of working alone, machine A is joined by machine B and together they complete the job at 6PM. How long would it have taken machine B to complete the job if it had worked alone for the entire job?