Josiah ran 4/5 mile. how many tenths are equal to 4/5 mile.

For this you will have to change the denominator and convert the 5ths to tenths. This is very simple
first put your fraction next to the denominator you are solving for
4
--    =       --
5             10

then ask you self how many fives go into ten? The answer should be two since 5x 2 equals ten. Then you go to your numerator and multiple the 4 by the same number. Thiss will get you 8. In the end, your fraction will be 
8
--
10 
which we now know is equivalent to 4/5
I apologize if this is a bit confusing but feel free to ask me any other questions regarding this method :)