Question

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?

Answer 1

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