Ten high-intensity bulbs are tested for 100 hours each. One failed at 10 hours; all others completed the test. Calculate FR(%), FR(N) and MTBF

What will be an ideal response?

FR(%) = 1/10 or 10%; operating hours = 9 × 100 + 10 = 910; FR(N) = 1/910 or .0011, and
MTBF = 910 hours