1. a) 315 + (146-x) = 401 b) 70-5.(x-3)= 45 c) x+(x+1)+(x+2)+….+(x+30)=1240 d)1+2+3+…+x=210 e) (x+1) . (2y-5)=143

1 bình luận về “1. a) 315 + (146-x) = 401 b) 70-5.(x-3)= 45 c) x+(x+1)+(x+2)+….+(x+30)=1240 d)1+2+3+…+x=210 e) (x+1) . (2y-5)=143”

1. $a)315+(146-x)=401$

   $⇒315+146-x=401$

   $⇒461-x=401$

   $⇒x=461-401$

   $⇒x=60$

   $b)70-5.(x-3)=45$

   $⇒5.(x-3)=70-45$

   $⇒5.(x-3)=25$

   $⇒x-3=25:5$

   $⇒x-3=5$

   $⇒x=5+3$

   $⇒x=8$

   $c)x+(x+1)+(x+2)+…+(x+30)=1240$

   $⇒31.x+(1+2+…+30)=1240$

   $⇒31.x+(30+1).30:2=1240$

   $⇒31.x+465=1240$

   $⇒31.x=1240-465$

   $⇒31.x=775$

   $⇒x=775:31$

   $⇒x=25$

   $d)1+2+3+…+x=210$

   $⇒(x+1).x:2=210$

   $⇒(x+1).x=210.2$

   $⇒(x+1).x=420$

   $⇒(x+1).x=21.20$

   $⇒x=20

   $e)(x+1).(2y-5)=143$

   => x+1 và 2y-5 là các cặp ước của 143

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