1. The problem statement, all variables and given/known data "A race car driver must average 180 km/h for 4 laps to qualify for a race. Because of engine trouble, the car averages only 150 km/h over the first 2 laps. What speed must be maintained for the last 2 laps?" 2. Relevant equations 3. The attempt at a solution So I do know the answer to be 225km/h but I don't quite understand why. Since half the time trial is completed with the driver being 30km/h below the needed average, wouldn't the 2nd half just be 30km/h above the needed average (210km/h for the last 2 laps)? I'm missing something here.