12.5+87.5÷1.25
=12.5+（100-12.5）x4/5
=12.5+80-10
=82.512.5+80-10是怎么来的？说清楚一点好吗？12.5+（100-12.5）x4/5=12.5+100x4/5-12.5x4/5=12.5+80-10