Question

[Bùi Phương Linh]

Tìm X :

 a, (X + 1 ) + (X + 4 ) + (X + 7 ) + (X + 10 ) + ... + (X + 28 ) = 155

Answer 1

[Vongola Tsuna]

x+1+x+4+x+7+x+10+...+x+28=155

10x + (1+4+7+10+...+28)=155

SSH :(28-1):3+1=10

TD (28+1)x10 :2=145

=> 10x + 145 = 155

10x=155-145

10x=10

x=10:10

x=1