Which ratio is greater? (i) (3 : 4) or (5 : 7) The given ratios are 3 : 4 and 5 : 7, which are equivalent to the fractions and respectively. Let us find the L.C.M. of 4 and 7: L.C.M. = 2 x 2 x 7 = 28. Clearly, . Hence, (3 : 4) (5 : 7). (ii) (11 : 21) or (19 : 28)