what is the speed of henry and kimball car

Question

Henry drives 12 miles per hour slower than Kimball. They started at the same spot, and drove in opposite directions. After 8.5 hours, they were 714 miles apart. Find each car’s speed.

Answer 1

Let's assume Kimball is driving at speed S, so Henry's speed is S-12. Since they're driving away from each other, the relative speed they're going is the sum of the independent speeds, 2S-12.

After 8.5 hours of driving, they're 714 miles apart. We can show this with the following equation:

(2S-12) * 8.5 = 714

Solving the quation:

17S - 102 = 714

17S = 612

S = 36

Kimball is traveling at 36 mph, and Henry is travelling at 24 mph