Hosting a 5k race, how long will the race be to the nearest tenth of a mile?

Now we already know
1 km = 0.6214 mile
Then 
5 km = ( 0.6214 * 5) miles
         = 3.107 miles
         = 3.11 miles
So the actual distance when converted to miles will be 3.11 miles. I hope this is the answer you were looking for. This is the simplest way for doing such problems and in future you can follow this method to find the answers without the need of any help.