Machine A takes 100 hours to complete a certain job and starts that job at 7AM. After two hour of working alone, machine A is joined by machine B and together they complete the job at 12PM. How long would it have taken machine B to complete the jobif it had worked alone for the entire job?
Select
A) 100.11
B) 10.98
C) 18.07
D) 45.01
E) 35.09
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 2 hr( so 2 units done) then A and B finish total work in 15 hours. Hence A and B finish 98 units in 15 hours. Of these 1x15=15 units were done by A. Hence B did 83units in 15 hours.   Hence B(working rate)= 83/15 units /hr   Hence B takes 100x15/83 = 18.07 hours to complete the job.   Answer 18.07.
<result>C</result>
Machine A takes 100 hours to complete a certain job and starts that job at 7AM. After two hour of working alone, machine A is joined by machine B and together they complete the job at 12PM. How long would it have taken machine B to complete the jobif it had worked alone for the entire job?