ITPEC FE Morning October 2021 Question 16

System Availability from Time Chart — calculate uptime ratio from a timeline.

Given a 300-hour timeline with shaded (working) and white (failure) segments:

• •Working periods: 0–60, 70–145, 150–240, 255–300
• •Uptime = 60 + 75 + 90 + 45 = 270 hours
• •Failure periods: 60–70, 145–150, 240–255
• •Downtime = 10 + 5 + 15 = 30 hours

Formula: Availability = uptime / total time

Availability = 270 / 300 = 0.90

Why not others:
- (a) 0.10 — this is the unavailability ratio (30 / 300)
- (b) 0.82 — no combination of segments produces this value
- (d) 0.98 — would require only 6 hours of downtime

Key rule: Availability = total working time ÷ total observed time. Read shaded vs white carefully — shaded = up, white = down.

AI-generated — may contain errors