Answer: 27 gallons
Explanation:
Since the car can go 35½ miles in 1½ miles gallons, we need to first calculate the number of miles that the car can go in 1 gallon. This will be:
= 35½ / 1½
= 71/2 / 3/2
= 71/2 × 2/3
= 23⅔ miles per gallon.
Therefore, the amount of gallons that the car need to go 639 miles will be:
= 639 / 23⅔
= 639 ÷ 71/3
= 639 × 3/71
= 27
The car will need 27 gallons.