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/x=45/5
b. 15/45=x/5
c. 15:45::x:5
d. 15/45=5/x

Answer 1

Correct answer: d.

Set up the proportional relationship (gallons : cost): 15/45 = 5/x. Cross-multiply: 15x = 45·5 = 225, so x = 225/15 = 15.

So 5 gallons cost $15.