A computer uses 2 W idle and 6 W active. If usage is 40% active and 60% idle, what is the average wattage?

A computer uses 2 W idle and 6 W active. If usage is 40% active and 60% idle, what is the average wattage?

• A. 4.0
• B. 3.0
• C. 3.6
• D. 4.8

Answer: (C)

Think of average power as a weighted average based on how long the computer is in each state. When active it uses 6 W, and when idle it uses 2 W. With 40% of time active and 60% idle, multiply and add: 6 W × 0.40 = 2.4 W from active, plus 2 W × 0.60 = 1.2 W from idle. Total = 3.6 W. So the average wattage is 3.6 W. If you compare other possibilities, a 50/50 split would give 4.0 W, a 25% active/75% idle would give 3.0 W, and a 70% active would give 4.8 W, which helps see why the given 40%/60% mix yields 3.6 W.

Think of average power as a weighted average based on how long the computer is in each state. When active it uses 6 W, and when idle it uses 2 W. With 40% of time active and 60% idle, multiply and add: 6 W × 0.40 = 2.4 W from active, plus 2 W × 0.60 = 1.2 W from idle. Total = 3.6 W. So the average wattage is 3.6 W.

If you compare other possibilities, a 50/50 split would give 4.0 W, a 25% active/75% idle would give 3.0 W, and a 70% active would give 4.8 W, which helps see why the given 40%/60% mix yields 3.6 W.