Question

简便计算：

1. 99.9*77.5+7.75

2. 0.42*160+36*1.6-31*3.2

3. （11.7+9.9）/0.9

4. 13.95/2-3.95*0.5

Answer 1

1. 99.9*77.5+7.75
＝999*7.75+7.75
＝7.75*（999+1）
＝7.75*1000
＝7750

2. 0.42*160+36*1.6-31*3.2
＝42*1.6+36*1.6-62*1.6
＝1.6*（42+36-62）
＝1.6*16
＝25.6

3. （11.7+9.9）/0.9
＝（117+99）/9
＝117/9+99/9
＝13+11
＝24

4. 13.95/2-3.95*0.5
＝13.95*0.5-3.95*0.5
＝（13.95-3.95）*0.5
＝10*0.5
＝5

Answer 2

1.99.9*77.5+7.75
=99.9*77.5+77.5*0.1=(99.9+0.1*77.5=100*77.5=7750
2.0.42*160+36*1.6-31*3.2
=42*1.6+36*1.6-62*1.6=(42+36-62)*1.6=16*1.6=25.6
3.(11.7+9.9)/0.9 =(11.7/0.9)-(9.9/0.9)=13-11=2
4.13.95/2-3.95*0.5=(13.95/2)-(3.95/2)=(13.95-3.95)/2=5

Answer 3

1. 99.9*77.5+7.75
=99.9*77.5+0.1*77.5
=(99.9+0.1)*77.5
=100*77.5
=7750

2. 0.42*160+36*1.6-31*3.2
=0.42*100*1.6+36*1.6-31*2*1.6
=42*1.6+36*1.6-62*1.6
=(42+36-62)*1.6
=16*1.6
=25.6

3. (11.7+9.9)/0.9
=11.7/0.9+9.9/0.9
=13+11
=24

4. 13.95/2-3.95*0.5
=13.95*1/2-3.95*1/2
=13.95*0.5-3.95*0.5
=(13.95-3.95)*0.5
=10*0.5
=5

Answer 4

1.99.9*77.5+7.75 =99.9*77.5+77.5 *0.1=100*77.5=7750

2. 0.42*160+36*1.6-31*3.2 = 0.42*160+0.36*160-0.62*160=0.16*160=25.6

3.（11.7+9.9）/0.9 =11.7/0.9+9.9/0.9=13+11=24

4 13.95/2-3.95*0.5=13.95/2-3.95/2=(13.95-3.95)/2=5

Answer 5

1. 99.9*10*7.75+7.75=(999+1)*7.75=7750