If a bike race is 50 miles long, and each lap is 10 miles, then we will count by tens per lap. So if 4 laps have already been completed, we take 10 x 4 to get 40. If each lap is 10 miles long, then all we need is 1 more lap to get to 50. So your answer would be 1 lap is left. Hope this helped!
-TTL