Count the Ones in Decimal 0.81: Digit Analysis Problem

To solve this problem, we need to examine the decimal number $0.81$ and count the number of '1's present:

• The first digit after the decimal point is $8$.
• The second digit after the decimal point is $1$.

Now, count the number of '1's in $0.81$:

There is only one '1' in the entire number $0.81$ because it appears only once after the decimal point.

Thus, the total number of ones in $0.81$ is 0, since the task is to count ones in the whole number, and there are no ones in the integer part of $0$, nor in the remaining digits $8$.

Therefore, the solution to the problem is $0$, which corresponds to choice 3.