1. 7/9 - 3/8 = (7·8 - 9·3)/(9·8) = (56 -27)/72 = 29/72
2. (5 4/5) - (2 1/4) = (5 - 2) + (4/5 - 1/4) = 3 + (4·4 -5·1)/(5·4) = 3 11/20
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(a/b) -(c/d) = (ad -bc)/(bd) . . . . a useful formula to remember when working problems like this. It is equivalent to multiplying the first fraction by d/d and the second one by b/b to get a common denominator of bd. Of course if the second fraction is added instead of subtracted, the sign changes in both places.
