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First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

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Yi Sun
Huizhou
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I think when reading the question I would clue in on the dates listed "from installation". The MTBF can also be considered Mean Life where the life of the asset in this case starts at installation. MTBF = Operating time / Number of Failures. This interpretation would use 23 months / 3 events.

I hope I am not leading you down the wrong path but this is how I would approach the problem. 

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Jesse Day


Original Message:
Sent: 06-22-2023 05:20 AM
From: Yi Sun
Subject: About MTBF

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

------------------------------
Yi Sun
Huizhou
------------------------------

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

Averaging the intervals works, but you left out the first one (9 months).  The average of 9, 7, 7 is 7.7 months. 

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks

I believe you could interpret this question a couple different ways. The first way is the first failure occurred at in 9 months and the next failure occurred 16 months later and the last failure occurred 23 months later. If that's the case the formula would be (9+16+23)/3=16 months MTBF.

Second interpretation, this is how I'm understanding the question, the first failure occurred in 9 months and the next failure occurred during the 16th month which is 7 months later and the last failure occurred during the 23rd month which was 7 months later than the 16th month. The formula would be (9+7+7)/3=7.67 months MTBF

I hope this helps.

Daniel Sallings

First all,thanks for your helping.

Here is a question in Practice Exam,"A machine requires repairs at the 9th month,16th month and 23rd month from installation.What is the Mean Time Between Failures(MTBF)?"

What I thought is 7 months,because each interval is 7 months,but the answer is 7.7 (23 months / 3 events).

Which number is right?

Thanks