数学简便运算(要写步骤）

题目

数学简便运算(要写步骤）
66.86-8.66-1.34
17.8/(1.78*4)
3.65*10.1
15.2/0.25/4
7.2*0.2+2.4*1.4
18-1.8/0.125/0.8
0.79*199
3.9/(1.3*5)
0.35*1.25*2*0.8
15/0.25

答案

66.86-8.66-1.34
=66.86-(8.66+1.34)
=66.86-10
=56.86
17.8/(1.78*4)
=17.8/1.78/4
=10/4
=2.5
3.65*10.1
=3.65*(10+0.1)
=3.65*10+3.65*0.1
=36.5+0.365
=36.865
15.2/0.25/4
=15.2/(0.25*4)
=15.2/1
=15.2
7.2*0.2+2.4*1.4
=2.4*3*0.2+2.4*1.4
=2.4*0.6+2.4*1.4
=2.4*(0.6+1.4)
=2.4*2
=4.8
18-1.8/0.125/0.8
=18-1.8/(0.125*0.8)
=18-1.8/0.1
=18-18
=0
0.79*199
=0.79*(200-1)
=0.79*200-0.79*1
=158-0.79
=157.21
3.9/(1.3*5)
=3.9/1.3/5
=3/5
=0.6
0.35*1.25*2*0.8
=(0.35*2)*(1.25*0.8)
=0.7*1
=0.7
15/0.25
=15/(0.5*0.5)
=15/0.5/0.5
=30/0.5
=60