Question

Shanika and Vanesa are comparing their electric bills for the past month. Shanika is on a standard use plan and Vanesa is on an interval use plan. Each person’s usage is listed on the chart below:

Standard Use Plan
Interval Use Plan
7.5 cents/kWh for the first 400 kWh
10 cents/kWh for the next 400 kWh
12.5 cents/kWh for anything over 800 kWh
On-peak hours - 15 cents/kWh
Off-peak hours - 3 cents/kWh

Both women use 1,325 kWh for the given 30 day period. Vanesa uses 500 kWh during on-peak hours and 825 during off-peak hours. Which person ends up paying more for their utilities? How much more?

Answer 1

Compute each bill.

Shanika (standard plan, 1,325 kWh):
- 1–400 kWh: 400 × $0.075 = $30.00
- 401–800 kWh: 400 × $0.10 = $40.00
- 801–1,325 kWh: 525 × $0.125 = $65.625
Total = $30.00 + $40.00 + $65.625 = $135.625 ≈ $135.63

Vanesa (interval plan, 500 on-peak, 825 off-peak):
- On-peak: 500 × $0.15 = $75.00
- Off-peak: 825 × $0.03 = $24.75
Total = $99.75

Shanika pays more. Difference = $135.625 − $99.75 = $35.875 ≈ $35.88.

So Shanika pays $35.88 more (exact difference $35.875).