Arranging these addends vertically may make the work easier:
13 5/12
-4 11/12)
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Since 11/12 is larger than 5/12, we must borrow from 13:
12 + 12/12 + 5/12
-4 -11/12
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8 17/12-11/12 = 8 6/12 = 8 1/2 = 8.5 (answers)