30-8.12-1.88
=30-(8.12+1.88)
=30-2
=28
18*205
=18*(200+5)
=18*200+18*5
=3600+90
=3690
250*125*32
=250*125*(4*8)
=(250*4)*(125*8)
=1000*1000
=1000000
13.015-(4.88-2.985)
=13.015-4.88+2.985
=(13.015+2.985)-4.88
=16-4.88
=11.12
0.75+57.88+2.25+0.12
=(0.75+2.25)+(57.88+0.12)
=3+58
=61