6.93*99+6.93
=6.93*(99+1)
=6.93*100
=693
12.5*3.4*0.8
=12.5*0.8*3.4
=10*3.4
=34
4.36*99+4.36
=4.36*(99+1)
=4.36*100
=436
8.7*9.9
=8.7*（10-0.1）
=87-0.87
=86.13
2.5*32*0.125
=2.5*4*8*0.125
=10*1
=10