直接计算:18/11+27/11+8/7=(18+27)/11+8/7=45/11+8/7=(45×7)/77+(8×11)/77=315/77+88/77=403/77
18/11+27/11+8/7=45/11+8/7=4又1/11+1又1/7=4又7/77+1又11/77=5又18/77