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Đáp án: + Giải thích các bước giải:

Câu `8)`

`a)` `x + 5, 84 = 9, 16`

`x - 9, 16 - 5, 84`

`x = 3, 32`

`b)` `x - 230 : 23 = 24`

` x - 230 = 24 xx 23`

`x - 230 = 552`

`x = 552 + 230`

`x = 782`

`c)` `( x - 230) : 23 = 24`

`(x - 230) = 24 xx 23`

`x - 230 = 552`

`x = 552 + 230`

`x = 782`

`d)` `9/2 - 2/5 xx x = 1`

`2/5 xx x = 9/2 - 1`

`2/5 xx x = 7/2`

`x = 7/2 : 2/5`

`x = 35/4`

`e)` `4/5 + 7/6 : x = 11/5`

`7/6 : x = 11/5 - 4/5`

`7/6 : x = 7/5`

`x = 7/6 : 7/5`

`x = 35/42 = 5/6`

`f)` `5/7 : x - 1 = 2/7`

`5/7 : x = 2/7 + 1`

`5/7 : x = 9/7`

`x = 5/7 : 9/7`

`x = 35/63 = 5/9`

Câu `9)`

`a)` `69, 78 + 35, 97 + 30, 22`

` = ( 69, 78 + 30, 22) + 35, 97`

` = 100 + 35, 97`

` = 135, 97`

`b)` `6/13 xx 5/7 + 6/13 xx 2/7 + 7/13`

` = 6/13 xx ( 5/7 + 2/7 ) + 7/13`

` = 6/13 xx 1 + 7/13`

` = 6/13 + 7/13`

` = 13/13 = 1`

`c)` `9/19 + 1, 251 + 10/19 - 1, 251`

` = ( 9/19 + 10/19) + ( 1, 251 - 1, 251)`

` = 1 + 0`

` = 1`

`d)` `8/15 xx 0, 25 - 1/4 xx 7/15 + 2, 75`

` = 8/15 xx 1/4 - 1/4 xx 7/15 +  11/4`

` = 1/4 xx ( 8/15 -  7/15)+  11/4`

` = 1/4 xx 1/15 + 11/4``

` = ( 1/4 + 11/4) xx 1/15`

` = 3 xx 1/15`

` = 3/15 = 1/5`

`#Ph`