Đáp án:

Bài `9` 

 `( 3 xx 7 xx 15 xx 8 ) / ( 5 xx 4 xx 27 xx 7)`

`=  ( 3 xx 7 xx 5 xx 3xx 2xx2xx2 ) / ( 5 xx 2xx2 xx 3 xx 3 xx 3 xx 7) `

`= ( \cancel{3}xx\cancel{7}xx\cancel{5}xx\cancel{3}xx\cancel{2}xx \cancel{2}xx2 )/(\cancel{5}xx\cancel{2}xx\cancel{2}xx\cancel{3}xx \cancel{3}xx3xx \cancel{7})`

`=2/3`

_______________________________-

 `( 9 xx 12 xx 5xx6 ) / ( 3 xx 18 xx 10 xx 12 )`

`=  ( 3 xx 3 xx 4 xx 3xx 5xx3xx2 ) / ( 3 xx 3xx3 xx 2 xx 5 xx 2 xx 4 xx 3)`

`=( \cancel{3}xx\cancel{3}xx\cancel{4}xx\cancel{3}xx\cancel{5}xx \cancel{3}xx \cancel{2})/(\cancel{3}xx\cancel{3}xx\cancel{3}xx\cancel{2}xx \cancel{5}xx\cancel{2}xx \cancel{4}xx2)`

`= 1/2`

Bài `10` 

`a)` `1268 + 99 + 501`

`= 1268 + (99+501)`

`= 1268 + 600`

`= 1868` 

`b)` `68 + 2080 + 32`

`= 2080 + ( 68 + 32)`

`= 2080 + 100`

`= 2180`

`c)` `121 + 85 + 115 + 469`

`= (121+469 ) + ( 85 + 115)`

`= 590 + 200 `

`= 790 `

Bài `9` :

`(3xx7xx15xx8)/(5xx4xx27xx7)`

``(cancel{3}xxcancel{7}xxcancel{3}xxcancel{5}xxcancel{2}xx2xx2)/(cancel{5}xxcancel{2}xxcancel{3}xxcancel{3}xx3xxcancel{7})`

`=(2xx2)/3`

`=4/3`

`(9xx12xx5xx6)/(3xx18xx10xx12)`

`=(cancel{3}xxcancel{3}xxcancel{3}xxcancel{4}xxcancel{5}xxcancel{2}xxcancel{3})/(cancel{3}xxcancel{3}xxcancel{3}xxcancel{2}xxcancel{2}xxcancel{5}xx2xxcancel{6})`

`=1/2`

_________________________________________________________________________________________

Bài `10` :

`a.1268+99+501`

`=1268+(99+501)`

`=1268+600=1868`

`b.68+2080+32`

`=(68+32)+2080`

`=100+2080`

`=2180`

`c.121+85+115+469`

`=(121+469)+(85+115)`

`=590+200=790`