Mike rode his bike 600 miles and he carried a spare tire on the trip. To provide equal wear on all 3 tires, he changed his tires while traveling. How many miles of wear did each tire accumulate?

• A. 300
• B. 1200
• C. 200
• D. 400

Answer: (D)

Key idea: wear is distributed only among tires that are on the road, and with a spare you can rotate so three tires share the wear.

Two tires are in contact with the road at any moment, so the total wear after traveling 600 miles is 2 × 600 = 1200 tire-miles. If this wear is split evenly among the three tires, each tire gets 1200 ÷ 3 = 400 miles of wear. So each tire accumulates 400 miles of wear. The other options don’t fit because they don’t reflect wear per tire when three tires share the load.