x + ( x + 1 ) + ( x + 2 ) + ..... + ( x + 10 ) = 1155
x + x + 1 + x + 2 + ....... + x + 10 = 1155
x . 11 + ( 1 + 2 + ..... + 10 ) = 1155
x . 11 + 55 = 1155
=> x . 11 = 1100
=> x = 100
Vậy: x = 100
ban oi tinh lai di 1100:11=110 chu ko fai 100
\(=x+\left(x+10\right)+\left(x+1\right)+\left(x+8\right)+..+\left(x+5\right)\)
\(=5\left(2x+10\right)+\left(x+5\right)\)
\(=11\left(x+5\right)=1155\)
suy ra \(x+5=105\Rightarrow x=100\)
\(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+10\right)=1155\)
\(\Leftrightarrow x+x+1+x+2+x+3+...+x+10=1155\)
\(\Leftrightarrow11x+\left(1+2+3+4+5+6+7+8+9+10\right)=1155\)
\(\Leftrightarrow11x+55=1155\)
\(\Leftrightarrow11x=1155-55\)
\(\Leftrightarrow11x=1100\)
\(\Leftrightarrow x=\frac{1100}{11}\)
\(\Leftrightarrow x=100\)
