Easy math question (that I sadly don't know)....?

Question

Michael drove to a friend's house at a rate of 40mi/h. He returned by the same route at a rate of 45 mi/h. The driving time for the round trip was 4h. What is the distance Michael traveled?

Answer 1

Say that there are x miles from Michael's house to his friend's house.

On his way to the friend's house, Michael has traveled x miles at a rate of 40m/h, so that has taken him x/40 hours.

On his way back home, Michael has traveled x miles again, but now at a rate of 45 m/h, therefore that has taken him x/45 hours.

But all the driving time is 4 hours, so we get the equation

x/40 + x/45 = 4

We multiply by 360 to get rid of the denominators and we get

9x + 8x= 1440

17x = 1440

x=1440/17 miles is the distance to the friend's house.

But Michael has gone there and then traveled back, so he traveled that distance twice. That's why the final answer is 2*1440/17=2880/17 miles

Hope that helps :)