If you simply want to compare these three numbers, the simplest way to
do is to calculate in mind. You see, 51 3/8 and 51 5/8, both of them
have the same denominator. So what you can do is to mutiply 4 to the
denominator of 51 1/2, and you will get 4/8. Then you simply need to
compare 4/8, 3/8 and 5/8. Then it is so obvious the number with 3/8 is
the smallest. It only takes a second to do it in mind. Of coz when you
have more complicated numbers, excel can be faster than us.