Make it an improper fraction by multiplying the whole number by the denominator then adding the numerator then find the common denominator (remember what you do to the bottom, you do to the top) then subtract normally.
eg. 1 4/5 - 1 7/10
= 9/5 - 17/10
= 18/10 - 17/10
= 1/10 or 0.1
Hope this helps!