1.(-81又18/25)÷20又1/4 =-81又18/25÷81/4=-81÷81/4-18/25÷81/4=-4-8/225=-4又8/2252.1/60÷（1/4-1/5+1/3) =1÷（1/4×60-1/5×60+1/3×60）=1÷（15-12+20）=1÷23=1/233.(1/4-1/5+1/3)÷1/60 =1/4×60-1/5×6...