Grades 3–5 · Societies
How can a water meter reading become a usage bill?
A water meter can record how much water has passed through it. A cumulative reading is a running total, not just the amount used today. Two readings in the same units can show use during the period between them.
In the diagramMeter difference → use → fictional chargeEarlier readingLater reading120126126 − 120 = 6 recorded unitsFixed: 4Usage: 12Total: 16Usage rate: 2 tokens per recorded unitInvented fixed-plus-usage bill; not a real tariff.
The fictional meter moves from 120 to 126. The difference is six units, so six units were recorded during that period. The larger reading does not mean that all 126 units were used in this one period.
The invented bill has a fixed charge of four tokens plus two tokens for each recorded unit. Six units add a usage charge of twelve, making a total of sixteen tokens. The fixed part stays separate from the multiplication.
This connects a measurement with one charging rule. Different utilities can use other rules and additional charges, so the token example is not a statement of anyone’s actual bill.
About this explanation
Starting knowledge: Subtract whole numbers and multiply a small use count by a stated rate.
Sources
- U.S. Environmental Protection Agency — Understanding Your Water Bill