`a, 989 + 0` và `0 + 989`

`405 + 165` và `165 + 405`

`(450 + 38) + 105` và `450+(38+105)`

`(231 + 153) + 924` và 231+(153+924)`

`b, 32 xx (15-6)`

`= 32 xx 9`

`= 288`

`244 - 124 : 4`

`= 244 - 31`

`= 213`

`180 : (3xx2)`

`= 180 : 6`

`=3 0`

127/128

      \(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\)

\(=\frac{1x64}{2x64}+\frac{1x32}{4x32}+\frac{1x16}{8x16}+\frac{1x8}{16x8}+\frac{1x4}{32x4}+\frac{1x2}{64x2}+\frac{1}{128}\)

\(=\frac{64}{128}+\frac{32}{128}+\frac{16}{128}+\frac{8}{128}+\frac{4}{128}+\frac{2}{128}+\frac{1}{128}\)

\(=\left(\frac{64}{128}+\frac{1}{128}\right)+\left(\frac{32}{128}+\frac{8}{128}\right)+\left(\frac{16}{128}+\frac{4}{128}\right)\)

\(=\frac{65}{128}+\frac{40}{128}+\frac{20}{128}\)

\(=125\)

a. 6916

b. 1532

48.(16+8)+32.14/16=48.24+32.14/16=100

toán 6 nha:

A=1/2+1/4+1/8+1/16+1/32+1/64+1/28

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

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

1/128+A=1/2+1/4+1/8+1/16+1/32+1/32

1/128+A=1/2+1/4+1/8+1/16+1/16

1/128+A=1/2+1/4+1/8+1/8

1/128+A=1/2+1/4+1/4

1/128+A=1/2+1/2

1/128+A=1

A=1-1/128

a=127/128