An engine oil saves 50 cents for every 25 miles of a trip. For a 500-mile trip the saving is $10, but the oil costs $20 and there is a $4 coupon. Is it worthwhile to buy the oil?

An engine oil saves 50 cents for every 25 miles of a trip. For a 500-mile trip the saving is $10, but the oil costs $20 and there is a $4 coupon. Is it worthwhile to buy the oil?

• A. Maybe
• B. No
• C. Yes
• D. Only if price drops

Answer: (B)

Comparing the money saved to the money spent determines whether it’s worthwhile. The oil saves 50 cents every 25 miles, which is 0.50/25 = 0.02 dollars per mile. For a 500-mile trip, that adds up to 0.02 × 500 = $10 saved. The oil itself costs $20, but a $4 coupon reduces the actual out-of-pocket to $16. So the net outcome is $10 saved minus $16 spent, which is -$6. Since you’d lose money instead of saving, buying the oil isn’t worthwhile.

Comparing the money saved to the money spent determines whether it’s worthwhile. The oil saves 50 cents every 25 miles, which is 0.50/25 = 0.02 dollars per mile. For a 500-mile trip, that adds up to 0.02 × 500 = $10 saved. The oil itself costs $20, but a $4 coupon reduces the actual out-of-pocket to $16. So the net outcome is $10 saved minus $16 spent, which is -$6. Since you’d lose money instead of saving, buying the oil isn’t worthwhile.