Question

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

Answer 1

=>( x + x + x +...+x ) + (1+2+3+....+29+30)=1240

=> 31x + ....tính vế phải....=1240

=> ...............Tự mà làm tiếp nhé!

Answer 2

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

=> 31x + (1+2+...+30) = 1240

=> 31x + 465 =1240

=> 31x = 775

=> x = 25

Answer 3

ta có x+(1+2+3+.....+30)

= 31X + 465 =1240

= 31X          =1240 - 465

= 31X          =775

=    X          =775/31

=    X          =25