What is the sum of 667 and 23?

Hint: To find the sum of 667 and 23, we have to add 667 and 23. We have to write 667 horizontally and in the next row we will write 23 horizontally under the same number of places. Then, we will put a ‘+’ sign on the left side and add. Then, we have to write the sum of these numbers in the bottom row. We will begin from the unit place. If the sum of the digits in all the places except the last place is a two digit number, we will have to add the tens place of this two digit number with the sum of the numbers in the next place. Here, we can see that 667 has the last place as hundredths. If the sum of the digits in hundreds places is a two digit number, we will have to write the number as it is.

Complete step-by-step solution:
We have to find the sum of 667 and 23. Here, ‘sum’ means addition. Therefore, we have to add 667 and 23. For this we will write 667 horizontally and in the next row we will write 23 horizontally under the same number places. Then, we will put a ‘+’ sign on the left side and add. This is illustrated below.
$\begin{align}
  & \text{ }\text{ }\begin{matrix}
   6 & 6 & 7 \\
\end{matrix} \\
 & +\begin{matrix}
   {} & 2 & 3 \\
\end{matrix} \\
 & \_\_\_\_\_\_\_\_\_\_ \\
\end{align}$
We will write the sum of these numbers in the bottom row. Now, let us add the numbers in the unit place. We know that $7+3=10$ . We will write the unit digit of 10 in the bottom row and the remaining digit will be carried to the sum of digits in the tens place and will be added with them.
$\begin{align}
  &\text{ }\text{ }\text{ } \text{ }\begin{matrix}
   {} &\color{red} 1 & {} \\
\end{matrix} \\
 & \text{ }\text{ }\begin{matrix}
   6 & 6 & 7 \\
\end{matrix} \\
 & +\begin{matrix}
   {} & 2 & 3 \\
\end{matrix} \\
 & \_\_\_\_\_\_\_\_\_\_ \\
 &\text{ } \text{ }\begin{matrix}
   {} & {} & \text{ }\text{ }\text{ } 0 \\
\end{matrix} \\
\end{align}$
The 1 in red colour is the carry over. Now, we have to add 6,2 and 1. We know that $6+2+1=9$ . Hence, we can write
$\begin{align}
  &\text{ }\text{ }\text{ } \text{ }\begin{matrix}
   {} & \color{red}1 & {} \\
\end{matrix} \\
 & \text{ }\text{ }\begin{matrix}
   6 & 6 & 7 \\
\end{matrix} \\
 & +\begin{matrix}
   {} & 2 & 3 \\
\end{matrix} \\
 & \_\_\_\_\_\_\_\_\_\_ \\
 & \text{ }\text{ }\begin{matrix}
   {} & 9 & 0 \\
\end{matrix} \\
\end{align}$
Now, we have to add the numbers in the hundredths place. We can see that only 6 is present in the hundredth place. Hence, the sum will be $6+0=6$ .
$\begin{align}
  & \text{ }\text{ }\text{ }\text{ }\begin{matrix}
   {} &\color{red} 1 & {} \\
\end{matrix} \\
 & \text{ }\text{ }\begin{matrix}
   6 & 6 & 7 \\
\end{matrix} \\
 & +\begin{matrix}
   {} & 2 & 3 \\
\end{matrix} \\
 & \_\_\_\_\_\_\_\_\_\_ \\
 &\text{ } \text{ }\begin{matrix}
   6 & 9 & 0 \\
\end{matrix} \\
\end{align}$
Hence, the sum of 667 and 23 is 690.

Note: Students must know that sum means addition, difference means subtraction, product means multiplication and quotient means division. They must never forget to add the carry of one place to the sum of numbers in the next place. If the sum of digits in the last place is a two digit number, we will have to write the number as it is.