The Sum of two integers
It's required to find the sum of 13 + 17
13
+ 17
-----------
First, we add the digits of the units. 3 + 7 = 10
Since the sum is greater than 9, we subtract 10 and account for a carry digit:
1 <-----carry from the previous sum
13
+ 17
-----------
0
Now we sum the digits of the tens: 1 + 1 + 1 = 3. Put that digit in place
13
+ 17
-----------
30
This is the final result: 30