Question

When a​ car's tire pressure is 30 pounds per square inch​ (psi), it averages 20.5 mpg of gasoline. If the tire pressure is increased to 35​ psi, the car averages 21.1 mpg of gasoline.

Answer parts ​a) through ​c).
​a) If someone drives an average of 23,000 mi per​ year, how many gallons of gasoline will he save in a year by increasing his tire pressure from 30 to 35​ psi?

b.) If gasoline costs ​$2.00 per​ gallon, how much will he save in a​ year?

c.)​ Assume that there are about 140million cars in a country and that these changes are typical of each​ car, how many gallons of gasoline would be saved if all drivers increased their​ cars' tire​ pressure?

Answer 1

For A, divide total miles by the miles per gallon for each tire pressure to find the number of gallons of gas used:

At 30 psi: 23000 / 20.5 = 1121.95 gallons , round to 1121 gallons.

At 35 psi: 23000 / 21.1 = 1090 gallons.

Number of gallons saved: 1121 - 1090 = 31 gallons.

B) multiply the cost per gallon by the number of gallons saved:

31 gallons x $2.00 = $62.00 saved.

C) Multiply the gallons saved by 1 car by total number of cars:

31 gallons x 140 million cars = 4,340 million gallons ( 4 billion 340 million gallons)