If the constant hazard model applies and FIT equals 250 failures per 10^9 hours, what is the hazard rate per hour λ?

• A. λ per hour = FIT × 10^-9; MTBF = 10^9 / FIT
• B. λ per hour = FIT × 10^-9; MTBF = FIT × 10^9
• C. λ per hour = FIT × 10^-6; MTBF = 10^6 / FIT
• D. λ per hour = FIT × 10^-3; MTBF = 10^3 / FIT

Answer: (A)

The key idea is converting a rate measured as FIT (failures in time) into a hazard rate per hour under a constant hazard model. FIT means failures per 10^9 hours. To get a per-hour hazard rate, multiply by 10^-9, giving λ = FIT × 10^-9 per hour. The mean time between failures (MTBF) is the reciprocal of the hazard rate, so MTBF = 1/λ = 10^9 / FIT hours.

With FIT = 250, λ = 250 × 10^-9 = 2.5 × 10^-7 per hour, and MTBF = 10^9 / 250 = 4 × 10^6 hours.

This matches the relationship λ per hour = FIT × 10^-9 and MTBF = 10^9 / FIT. The other scalings (such as ×10^-6 or ×10^-3) would misconvert the FIT unit.