12.5x2.5x2.5=(12+0.5)x(6十0.25)=72十3十3+0.125=78.125
根据题意，计算如下5x2.5x2.5=5x5/2x5/2=125/4=31.25
12.5x2.5x2.5=12.5x(2+0.5)x(2+0.5)=12.5x(4+2+0.25)=12.5x6+12.5x(0.2+0.05)=75+2.5+0.625=77.5+0.625=78.125
