When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 3+1=4\)

\(\displaystyle \frac{\begin{array}[b]{r}20\\ +\ 10\end{array}}{ \ \ \ \space40}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 3+1=4\)

\(\displaystyle \frac{\begin{array}[b]{r}35\\ +\ 10\end{array}}{ \ \ \ \space45}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 4+1=5\)

\(\displaystyle \frac{\begin{array}[b]{r}40\\ +\ 10\end{array}}{ \ \ \ \space50}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 4+1=5\)

\(\displaystyle \frac{\begin{array}[b]{r}45\\ +\ 10\end{array}}{ \ \ \ \space55}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 5+1=6\)

\(\displaystyle \frac{\begin{array}[b]{r}50\\ +\ 10\end{array}}{ \ \ \ \space60}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 5+1=6\)

\(\displaystyle \frac{\begin{array}[b]{r}55\\ +\ 10\end{array}}{ \ \ \ \space65}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 6+1=\)\(\displaystyle 7\)

\(\displaystyle \frac{\begin{array}[b]{r}60\\ +\ 10\end{array}}{ \ \ \ \space70}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 6+1=\)\(\displaystyle 7\)

\(\displaystyle \frac{\begin{array}[b]{r}65\\ +\ 10\end{array}}{ \ \ \ \space75}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 7+1=8\)

\(\displaystyle \frac{\begin{array}[b]{r}70\\ +\ 10\end{array}}{ \ \ \ \space80}\)

When we add \(\displaystyle 10\) to a two digit number, the only number that changes in our answer is the tens position, and it will always go up by \(\displaystyle 1\). Mentally, we can add \(\displaystyle 1\) to the number in the tens place to find our answer. 

\(\displaystyle 7+1=8\)

\(\displaystyle \frac{\begin{array}[b]{r}75\\ +\ 10\end{array}}{ \ \ \ \space85}\)