Digital PSAT Math Practice Question 94: Answer and Explanation

Question: 94

Linda's 15-gallon car tank has only 2 gallons left when she pulls into a gas station. She wants to purchase only the gas she will need to drive 240 miles and still have 1 gallon remaining. Her car gets 28 miles to the gallon. How many gallons should Linda purchase, to the nearest tenth of a gallon?

• A. 6.6 gallons
• B. 7.6 gallons
• C. 8.6 gallons
• D. 9.6 gallons

Correct Answer: B

Explanation:

(B) If you were told that you had to travel 50 miles and that your car got 10 miles/gallon, you may intuitively see that you need 5 gallons of gas. You get that by dividing 50/10. Following this logic, we can get the number of gallons of gas Linda needs to travel 240 miles by dividing 240 by 28:

If this doesn't quite make sense, you could also do dimensional analysis to cancel out the units you don't want. You want to cancel out miles and end up with gallons:

Linda also wants to have 1 gallon left, so she'll want to have 9.57 gallons in her tank when she starts out. Linda already has 2 gallons in her tank, so she needs to buy 9.57 - 2 = 7.57 gallons, or 7.6 rounded to the nearest tenth. This matches choice (B).