Question

It took Gustavo 5 hours to drive to a job interview. On the way home, he was able to increase his average speed by 20mph and make the return drive in only 3 hours. Find his average speed on the return drive.

Answer 1

His average speed on the return drive is:

50 mph

Explanation:

Let d be the distance from home to the place of his job interview.

Let s be the average speed when he drive to his job interview.

Now, it is given that:

It took Gustavo 5 hours to drive to a job interview.

We know that distance is the product of speed and time.

i.e.

`Distance=Speed* Time`

Hence, we have:

`d=5s--------(1)`

Also,

On the way home, he was able to increase his average speed by 20 mph and make the return drive in only 3 hours.

His average speed back home is: s+20

and his time is: 3 hours

Hence, we have:

`d=3(s+20)\\\\i.e.\\\\d=3s+60----------(2)`

From equation (1) and equation (2) we have:

`5s=3s+60\\\\i.e.\\\\5s-3s=60\\\\2s=60\\\\s=(60)/(2)\\\\s=30\ mph`

Hence, his average speed on the return drive is: s+20

= 30+20

= 50 mph