\(\left(y+1\right)+\left(y+4\right)+\left(y+7\right)+....+\left(y+31\right)=231\)
\(\Rightarrow\left(y+y+...+y\right)+\left(1+4+7+...+31\right)=231\)
\(\Rightarrow11y+176=231\)
\(\Rightarrow11y=231-176\)
\(\Rightarrow11y=55\)
\(\Rightarrow y=55:11\)
\(\Rightarrow y=5\)
Vậy y = 5
(y+1)+(y+4)+(y+7)+..........+(y+31)=231
y+1+y+4+y+7+y+10+..........+y+31=231
(y+y+y+y+........+y+y)+(1+4+7+10+....+31)=231
y*11+176=231
y*11=231-176
y*11=55
y=55 :11
y=5
vậy y=5