Question

You fill your car with 15 gallons of gas at a cost of $45. Using fractional notation, how do you write a proportion that shows how much 5 gallons of gas will cost? Use x to represent the unknown cost. a. 15:45::x:5 b. 15/45=5/x c. 15/45=x/5 d. 15/x=45/5

Answer 1

Answer: b.

Set up proportionality: 15 gallons / $45 = 5 gallons / x. Cross-multiply: 15x = 45·5 = 225, so x = 225/15 = 15. Thus 5 gallons cost $15.