What is better a car that gets 15 miles per gallon at 2.20 per gallon or a car that gets 14.7 miles per gallon at 1.70 per gallon?

Answer 1

Assuming you mean better that the car is cheaper to run:

Divide any distance by the mpg to get the number of gallons for that distance and multiply by the cost per gallon for the two different mpg and associated fuel cost to find the total cost of going that distance; the cheaper option will be obvious.

15 miles at 15 mpg with 1 gal costing $2.20 costs a total of: 15 miles ÷ 15 mpg × $220/gal = $2.20

15 miles at 14.7 mpg with 1 gal costing $1.70 costs a total of: 15 miles ÷ 14.7 mpg × $1.70/gal ≈ $1.73

$1.73 < £2.20 → the lower mpg at 14.7 mpg is cheaper to run when it costs $1.70 per gallon

Answer 2

14.7 gallons at 1.70 is cheaper for you to run though that does not make it a better car.