First we will convert all the given fractions in (a/b) form if they are not in the same form.
257=2×7+57=197278=2×8+78=238So,the fractions are,197,187,58,4314,238L.C.M of 7,8,14=56
Converting all the given fractions into equivalent fractions.
19×87×8=1525618×87×8=144565×78×7=355643×414×4=1725623×78×7=161563556<14456<15256<16156<17256
Therefore,
The sum of the greatest fraction and smallest = 3556+17256=35+17256=20756
The difference between the greatest and smallest fraction
=17256−3536=172−3556=13756