A race car driver must average 200 km/hr for four laps to qualify for a race. because of engine trouble, the car averages only 170 km/hr over the first two laps. what average speed must be maintained for the last two laps?

To know the average, let us assign values for each of the four laps as x, y, v and w. The average of the first two is 170. So, we can determine the sum of x and y:

(x+y) / 2 = 170

x = y = 340

Next, we have to find the value for (v+w):

(x+y+v+w) / 4 = 200

[340 + (v+w) ]/4 = 200

v+w = 460

So, we can now determine the average of the last two laps:

Average = (v+w) / 2 = 460/2 = 230 km/h