A10 ft fence is 8 in .long on the scale drawing. what is the scale drawing?

To find scale we have to provide common unit, so inches.
10 foot = 120 inch becauyse 1 foot = 12 inch so 
10foot*12=120 ich
Now
8 inch in drawing is 120 in real, so the scale is 8:120

Think of it this way:

10 (ft)    120 (in)  -> 10 ft is equal to 120 in
    x           8 (in)    -> x ft is equal to 8 in

so then all you have to do is find the value of x, you do this by multiplying 10*8 (=80) and dividing that by 120, which as a fraction will give you 

 80
, you can even simplify (divide both terms by 10 [to remove the 0's],   120    then divide them again by 4) this and it will give you the final result of              2/3. That will be the scale.