用简便方法计算下面各题、求答案我弟的作业,不是拿来抄的,

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用简便方法计算下面各题、求答案
我弟的作业,不是拿来抄的,

75*102
=75*100+75*2
=7500+150
=7650
1.2*2.5
=2.5*4*0.3
=10*0.3
=3
6.74*1.8-1.8*1 .74
=1.8*(6.74-1.74)
=1.8*5
=8
(1/6+1/4-1/8)*480
=1/6*480+4/1*480-1/8*480
=80+120-60
=140
90.1-9.9
=90.1-10+0.1
=80.1+0.1
=80.2
90.1*9.9
=90.1*10-90.1*0.1
=901-9.01
=891.9
7001-387-213
=7001-(387+231)
=7001-600
=6401
77/8/125
=77/(8*125)
=77/1000(分数)
3.54*99+3.54
=3.54/(99+1)
=3.54*100
=354
272*125
=34*(8*125)
=34*1000
=34000
0.38*3.5+0.038*65
=0.038*35+0.038*65
=0.038*(35+65)
=0.038*100
=3.8
21+22+23+24+...+100
=(21+100)*40
=121*40
=4840