ISRO2020-67

Question

What is the availability of the software with the following reliability figures

Mean Time Between Failures (MTBF) is $20$ days

Mean Time To Repair (MTTR) is $20$ hours

• A. $90\%$
• B. $96\%$
• C. $24\%$
• D. $50\%$

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https://www.geeksforgeeks.org/gate-gate-it-2004-question-72/

Answer 1

GIven MTBF = 20 days = $20\times24 = 480$ hours.
MTTR = 20 hours.

$Availability = \frac{MTBF}{MTBF+MTTR}\times100$
$\rightarrow\frac{480}{480+20}\times100=\frac{480}{500}\times10=96\%$

Option B

Answer 2

GIven MTTR = 20 hrs , MTBF = 20 days , converting it to hrs we get 20*24 =480 hrs , now MTTF= MTBF-MTTR =n480-20=460. , Availability we have = MTTF/MTBF = 460/480 = 0.958 approximately = 96%