Question

Tìm x, biết:

x+(x+1)+(x+2)+...+(x+30)=1240

Answer 1

`x+(x+1)+(x+2)+...+(x+30)=1240`

`=> (x + x + x + ... + x) + (1 + 2 + 3 +... + 30) = 1240`

`=> 31x + 465 = 1240`

`=> 31 x = 1240 - 465`

`⇒ 31x = 775`

`⇒ x = 775 : 31` 

`⇒ x = 25`

Answer 2

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\\ \left(x+x+...+x\right)+\left(1+2+...+30\right)=1240\\ 31x+465=1240\\ 31x=1240-465\\ 31x=775\\ x=775:31\\ x=25\)

Answer 3

\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\)

\(\Leftrightarrow\left(x+x+...+x\right)+\left(1+2+...+30\right)=1240\)

\(\Leftrightarrow31x+465=1240\)

\(\Leftrightarrow x=25\)