7.8*80+6.5
=1.3*5*6*16+6.5
=6.5*（96+1）
=6.5*97
=6.5*（100-3）
=6.5*100-6.5*3
=650-19.5
=630.5
0.85*0.5+0.25*3
=0.85*0.5+0.5*0.15
=（0.85+0.15）*0.5
=1*0.5
=0.50.5*0.15不等于0.25*37.8*80+6.5=1.3*5*6*16+6.5=6.5*（96+1）=6.5*97=6.5*（100-3）=6.5*100-6.5*3=650-19.5=630.50.85*0.5+0.25*3=0.25*1.7+0.25*3=0.25*（1.7+3）=0.25*4+0.25*0.7=1+0.175=1.175看错小数点了