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.

Answer 1

Their speeds are 45 mi/hr and 49 mi/hr

Answer 2

The speed of the faster car is 68 miles/hr and speed of slower car is 40 miles/hr.

Explanation:

Let the speed of the slower car be x

Now we are given that The speed of the faster car was 12 mph less than twice the speed of the other one.

So, Speed of faster car = 2x-12

Now we are given that 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.

So, faster car completes the journey in 6 hours

Distance =
`Speed * Time`

So, Distance traveled by faster car =
`(2x-12)* 6`

Distance traveled by slower car in 6 hours =
`Speed * Time=6x`

Since we are given that when faster car completes the journey at that time slower car was 168 miles away from the destination .

A.T.Q

`(2x-12)* 6-6x=168`

`12x-72-6x=168`

`6x-72=168`

`6x=240`

`x=(240)/(6)`

`x=40`

So, speed of slower car is 40 miles/hr.

Speed of faster car = 2x-12 =2(40)-12=80-12=68 miles/hr.

Hence the speed of the faster car is 68 miles/hr and speed of slower car is 40 miles/hr.