Question

速算与巧算～～

0.38×35/5＋0.038÷0.25＋38×0.02

17171717
--------
29292929

1966+1976+1986+1996+2006

100-98+96-94+92-90+…+8-6+4-2

1+2+3+…+99+100+99+98+…+1

Answer 1

0.38×35/5＋0.038÷0.25＋38×0.02 =0.38*7+0.038*4+38*0.02
=0.38*（7+0.4+2）=0.38*9.4=3.572
17171717 17*1010101
-------- =----------=17/29
29292929 29*1010101
1966+1976+1986+1996+2006 =1986-20+1986-10+1986+1986+10+1986+20
=1986*5=9930
100-98+96-94+92-90+…+8-6+4-2 =2+2+2+…+2（25个2）=50
1+2+3+…+99+100+99+98+…+1=(1+100)*50*2=11500

Answer 2

1966+1976+1986+1996+2006=（1966+2006）+（1976+1996）+1986=1986*5=9930

100-98+96-94+92-90+…+8-6+4-2 =（100-98）+（96-94）+（92-90）+…+（8-6）+（4-2 ）=50*2=100

1+2+3+…+99+100+99+98+…+1=1+2+3+…+99+100
+99+98+…+1
=100+100+100...+100
=100*100
=10000
其他没看懂，1应该提取个38出来

Answer 3

0.38×35/5＋0.038÷0.25＋38×0.02
=0.38×(35/5+2/5+2)
=0.38×47/5=0.38*9.4=3.572

17171717 1010101*17 17
-------- =--------------- = ----
29292929 1010101*29 29

1966+1976+1986+1996+2006
=2000-34+2000-24+2000-14+2000-4+2000+6
=5*2000-70=9930

100-98+96-94+92-90+…+8-6+4-2
=(100-98)+(96-94)+(92-90)+…+(8-6)+(4-2)
=25*2=50

1+2+3+…+99+100+99+98+…+1
=(1+99)+(2+98)+...+(98+2)+(99+1)+100
=100*100=10000