We can find the sum of a one-digit and a two-digit number by regrouping.
For example: Let's find the sum of 11 and 9.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
The correct answer is
The smallest number is the one that comes first while counting.
To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.
21 is the smallest number.