Question

(x+1)+(x+2)+(x+3)+.....+(x+10)=255

Answer 1

( x + 1 ) + ( x + 2 ) + ( x + 3 ) + ..... + ( x + 10 ) = 255

=> x + 1 + x + 2 + x + 3 + .................. + x + 10 = 255

=> 10x + ( 1 + ........... + 10 ) = 255

                10x + 55 = 255

                        10x = 255 - 55 = 200

                            x = 200 : 10 = 20

Chắc z 

Answer 2

<=>10x+(1+2+3+4+5+6+7+8+9+10)=255

<=> 10x+55=255

<=>10x = 255-55

<=> 10x=200

 =>    X=200:10=20