Once you learn the pattern it becomes very easy to count by tens to 100.
Each number will end in zero, and the first digit equal the previous digit plus 1.
For example: 10 then take 1+1 = 2 and add a zero = 20
Next, take 20 then take 2 + 1 = 3 then add a zero to get 30
Continue this pattern to 100
Lets count by tens to 100 with numbers.
Lets count by tens to 100 with words.
Counting by Tens chart