Question

Two cars started moving from San Jose to San Diego. The speed of the faster car was 12 mph less than twice the speed of the other one. In 6 hours the faster car got to San Diego, and by that time the slower one still was 168 miles away from the destination. Find their speeds. Please help, all the other answers were incorrect.

Answer 1

40 mph and 68 mph

Explanation:

Let x mph be the speed of the slower car, then 2x-12 mph is the speed of the faster car.

In 6 hours the faster car got to San Diego, so it travels the distance

`6\cdot (2x-12)=12x-72\ miles.`

By that time the slower car was 168 miles away from the destination, so the slower car travels the distance

`12x-72-168=2x-240\ miles`

It takes the slower car 6 hours to travel 12x-240 miles, so

`6x=12x-240\\ \\6x-12x=-240\\ \\-6x=-240\\ \\6x=240\\ \\x=40\ mph.`

Now,

`2x-12=2\cdot 40-12=80-12=68\ mph`