GMATT73 wrote:

The average speed of a car decreased by 3 miles per hour every successive 8-minute interval. If the car traveled 4.8 miles in the sixth 8-minute interval, what was the average speed of the car, in miles per hour, in the first 8-minute interval?

A. 35

B. 40

C. 48

D. 51

E. 53

Assume the speed was X in the first 8-minute interval

So the speed would be x-3 after first interval

....................

So the speed will be x-15 at the 6th interval

Now,

Rate x Time = Distance

(X-15) x 8 min = 4.8 miles

> (x-15) x 8/60 hours = 4.8 miles

> X-15 = (4.8) x 60/8= 36

> X=36+15= 51

Ans D