解
36.9-10.47+3.1-0.53
=(36.9+3.1)-(10.47+0.53)
=40-11
=29
2.5*3.2*1.25
=2.5*4*8*1.25
=(2.5*4)*(8*1.25 )
=10*10
=100
9.9*34
=(10-0.1)*34
=10*34-0.1*34
=340-3.4
=336.6
3.12+3.12*99
=3.12*(1+99)
=3.12*100
=312
3.12*1.2+6.88*1.2
=(3.12+6.88)*1.2
=10*1.2
=12