A certain highway has a service station once every 12 miles,

[marie922]

A certain highway has a service station once every twelve miles, a restaurant once every fifteen miles, and a rest area once every twenty miles. How often is there a location with all three at the same location?

I'm afraid I don't understand what they're looking for. Are they perhaps wanting me to find the number of miles between the locations with all three things...?

Thank you for your help!

 

[Mrspi]

Yes, they're wanting the distance (number of miles) between locations with all three things.

Here's a hint: think about common multiples of the distances.