`4 5/9 : -5/7 + 49/9 : -5/7`

`3/8 - ( 1,2 - 5/8 )`

`10 2/5-3,75-6,25`

`(-9/7)+(-1,23)-(-2/7)-0,77`

6a + a8 .... (a +6) x 11

`x-7/2=3/4`

`x=3/4+7/2`

`x=3/4+14/4`

`x=17/4`

`h) 1999 . 7 + 1999 +1999 . 2`

`= 1999 xx (7 + 1 + 2)`

`= 1999 xx 10`

`= 19990`

Xin phép sửa `1` chút `:` `1/2+1/4+1/8+1/16+1/32+1/64+1/128`

Đặt `A=1/2+1/4+1/8+1/16+1/32+1/64+1/128`

`2A=2(1/2+1/4+1/8+1/16+1/32+1/64+1/128)`

`2A=1+1/2+1/4+1/8+1/16+1/32+1/64`

`2A-A=(1+1/2+1/4+1/8+1/16+1/32+1/64)-(1/2+1/4+1/8+1/16+1/32+1/64+1/128)`

`A=1-1/128`

`A=127/128`

`I)1/2.3+1/3.4+1/4.5+1/5.6+1/6.7`

`=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7`

`=1/2-1/7`

`=5/14`

`n)2,75.67+0,13.125+2,75.33+125.0,67`

`=2,75.(67+33)+125.(0,13+0,67)`

`=2,75.100+125.0,8`

`=275+100`

`=375`

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