You have to subtract 5/4 by 2/3 but in order to do that you must find a common denominator or least common multiple so the least common denominator of 4 and 3 is 12 so you have to multiply 4 by 3 and three by 4 to make both denominators 12 but you have to do the same thing on the top as you did the bottom so:
5/43= 15/12 and 2/34=8/12
Then 15/12-8/12 is 7/12 so Jim has to run 7/12 more
