Multiply the top and bottom of 5/9 by 12 and the top and bottom of 7/12 by 9 to get:
5*12/(9*12) and 7*9/(12*9)
The bottom of both are now the same, so just compare the tops, which are:
5*12 = 60 and 7*9 = 63
5*12 is smaller than 7*9 so 5/9 is smaller than 7/12
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