先算乘法再通分做加法11/42+4/5×5/12+4/7=11/42+1/3+4/7=11/42+14/42+24/42=49/42
11/42+4/5×5/12+4/7=11/42+1/3+4/7=11/42+14/42+24/42=49/42=7/6