Given,
Availability = 90%
MTBF = 200 Days=200*24=4800 Hours.
As we know that,
Availability = MTBF*100/MTBF+MTTR
90 = 4800*100/4800+MTTR
432000+90MTTR = 480000
90MTTR = 480000-432000
90MTTR = 48000
MTTR = 48000/90
MTTR = 533.33 Hours.
According to question, we have to find MTBF,
It is given that, MTTR is increased by 5 Days = 5*24=120 hours.
Availability = MTBF*100/MTBF+MTTR
95 = MTBF*100/MTBF+533.33+120
95 = 100MTBF/MTBF+653.33
95MTBF + 62066.35 = 100MTBF
62066.35 = 100MTBF – 95MTBF
62066.35 = 5MTBF
62066.35/5 = MTBF
MTBF = 12413.27 Hours
Convert it into Days,
MTBF = 12413.27/24
MTBF = 517.21 Days
So, Option C is the Correct Answer.