True net savings
$4.00
Store B wins after travel and time.
Basket savings
$13.00
Fuel cost
$1.50
Time cost
$7.50
Quick answer: A second store saves money only when the basket-price difference exceeds extra fuel, travel time, fees, and other trip costs.
Evergreen method
Compare usable cost, not package price
The durable comparison is price per common unit adjusted for the share you will actually use.
Formula
usable unit cost = price ÷ (quantity × usable share)Reproducible steps
- 1.Convert every option to the same unit.
- 2.Estimate the share your household will use before spoilage.
- 3.Choose the lower usable unit cost only if storage and cash flow also work.
Data note — Evergreen model: The formula works with your own inputs and does not depend on a specific price or year.
Related
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