Bài 1:Tìm * a)123-5x(*+4)=38 b)70-5x(*-3)=45 c)71+(26-3x*):5=75

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1. $\text { a) 123 – 5 x (* + 4) = 38 }$

   $\text { 5 x (* + 4) = 123 – 38 }$

   $\text { 5 x (* + 4) = 85 }$

   $\text { * + 4 = 85 : 5 }$

   $\text { * + 4 = 17 }$

     $\text { * = 17 – 4 }$

     $\text { * = 13 }$

   $\text { b) 70 – 5 x (* – 3) = 45 }$

   $\text { 5 x (* – 3) = 70 – 45 }$

   $\text { 5 x (* – 3) = 25 }$

   $\text { * – 3 = 25 : 5 }$

   $\text { * – 3 = 5 }$

     $\text { * = 5 + 3 }$

     $\text { * = 8 }$

   $\text { c)  71 + (26 – 3 x *) : 5 = 75 }$

   $\text { (26 – 3 x *) : 5 = 75 – 71 }$

   $\text { (26 – 3 x *) : 5 = 4 }$

   $\text { 26 – 3 x * = 4 x 5 }$

   $\text { 26 – 3 x * = 20 }$

     $\text { 3 x * = 26 – 20 }$

     $\text { 3 x * = 6 }$

     $\text { * = 6 : 3 }$

     $\text { * = 2 }$

   Trả lời

2. `a)123-5xx(x+4)=38`

   `5xx(x+4)=123-38`

   `5xx(x+4)=85`

   `x+4=85:5`

   `x+4=17`

   `x=17-4`

   `x=13`

   `b)70-5xx(x-3)=45`

   `5xx(x-3)=70-45`

   `5xx(x-3)=25`

   `x-3=25:5`

   `x-3=5`

   `x=5+3`

   `x=8`

   `c)71+(26-3xxx):5=75`

   `(26-3xxx):5=75-71`

   `(26-3xxx):5=4`

   `26-3xxx=4xx5`

   `26-3xxx=20`

   `3xxx=26-20`

   `3xxx=6`

   `x=6:3`

   `x=2`

   Trả lời