3. A reliability test is run for 5000 hours. There are four (4) failures, all happening

sometime in the first 4500 hours. Then, the test was run for an additional 500 hours

with no more failures. In other words, this was a time-terminated 5000 hour test with

4failures.

For a time-terminated test with four (4) failures, how many degrees of freedom (v)

does this represent?

Using Chi-Squared, calculate the lower confidence level MTBF for a 60%

confidence level (40% risk factor) for this test.

The same test was continued to 7631 hours (2631 additional hours) with no additional

failures.

Using Chi-Squared, calculate the lower confidence level MTBF for a 90%

confidence level (10% risk factor) for this test.

Compare your two MTBF answers, and comment on how this illustrates a way of

increasing the confidence level of a test from 60% to 90%