1. $\begin{array}{r}
&11\\
+\!\!\!\!\!\,&12\\
\hline
\end{array}$
Answer: 23
Explanation:
$\begin{array}{l}
11 + 12 &= 11 + (10 + 2)\\
&= 21 + 2\\
&= 23
\end{array}$
2. $\begin{array}{r}
&12\\
+\!\!\!\!\!\,&14\\
\hline
\end{array}$
Answer: 26
Explanation:
$\begin{array}{l}
12 + 14 &= 12 + (10 + 4)\\
&= 22 + 4\\
&= 26
\end{array}$
3. $\begin{array}{r}
&13\\
+\!\!\!\!\!\,&14\\
\hline
\end{array}$
Answer: 27
Explanation:
$\begin{array}{l}
13 + 14 &= 13 + (10 + 4)\\[6px]
&= 23 + 4\\[6px]
&= 27
\end{array}$
4. $\begin{array}{r}
&12\\
+\!\!\!\!\!\,&17\\
\hline
\end{array}$
Answer: 29
Explanation:
$\begin{array}{l}
12 + 17 &= 12 + (10 + 7)\\[6px]
&= 22 + 7\\[6px]
&= 29
\end{array}$
5. $\begin{array}{r}
&13\\
+\!\!\!\!\!\,&15\\
\hline
\end{array}$
Answer: 18
Explanation:
$\begin{array}{l}
13 + 15 &= 13 + (10 + 5)\\[6px]
&= 23 + 5\\[6px]
&= 28
\end{array}$
6. $\begin{array}{r}
&16\\
+\!\!\!\!\!\,&13\\
\hline
\end{array}$
Answer: 29
Explanation:
$\begin{array}{l}
16 + 13 &= 16 + (10 + 3)\\[6px]
&= 26 + 3\\[6px]
&= 29
\end{array}$
7. $\begin{array}{r}
&19\\
+\!\!\!\!\!\,&12\\
\hline
\end{array}$
Answer: 31
Explanation:
$\begin{array}{l}
19 + 12 &= 19 + (10 + 2)\\[6px]
&= 29 + 2\\[6px]
&= 31
\end{array}$
8. $\begin{array}{r}
&18\\
+\!\!\!\!\!\,&12\\
\hline
\end{array}$
Answer: 30
Explanation:
$\begin{array}{l}
18 + 12 &= 18 + (10 + 2)\\[6px]
&= 28 + 2\\[6px]
&= 30
\end{array}$
9. $\begin{array}{r}
&14\\
+\!\!\!\!\!\,&18\\
\hline
\end{array}$
Answer: 32
Explanation:
$\begin{array}{l}
14 + 18 &= 14 + (10 + 8)\\[6px]
&= 24 + 8\\[6px]
&= 32
\end{array}$
10. $\begin{array}{r}
&15\\
+\!\!\!\!\!\,&17\\
\hline
\end{array}$
Answer: 32
Explanation:
$\begin{array}{l}
15 + 17 &= 15 + (10 + 7)\\[6px]
&= 25 + 7\\[6px]
&= 32
\end{array}$