How much was the natural gas bill for same period last year?

Question

this year cu. ft. used 21,500          Cost this year $90.12

service days  30

cost: 40.52cents/100 cu. ft.

service charge:  $3.00

Avg. 100 cu.ft./day for service period:  current-7    last year- 8

Answer 1

Number of cubic feet of gas used =21,500 which is 215 units of 100 cubic feet.

Cost per 100 cubic feet=$0.4052, so cost for 215 units=$87.118.

Add on the $3 service charge for the period of 30 days=$90.118 which rounds up to $90.12 as indicated.

Average current consumption is 215/30=7.17 units (1 unit=100cubic feet) per day. The given figure of 7 approximates to this

Average consumption last year was 8 units per day=240 units in 30 days. If we use this as the actual number of units consumed, and cost per unit was $0.4052 (same as current), then the cost for 240 units was $97.248. Add the $3 service charge and we get $100.25 (rounded) as last year's cost for gas. Given that there was an error in the current estimate of the average daily consumption (given 7 rather than 7.17), we could assume the same error last year, in which case the consumption in 30 days could be as high as 246 units, resulting in a cost of $99.56 plus $3 service charge=$102.56.