To find out what you need to add to \( \frac{4}{5} \) to get 1 whole, you can set up the equation:
\[ \frac{4}{5} + x = 1 \]
To solve for \( x \), subtract \( \frac{4}{5} \) from both sides:
\[ x = 1 - \frac{4}{5} \]
Convert 1 to a fraction with a denominator of 5:
\[ 1 = \frac{5}{5} \]
Now, subtract:
\[ x = \frac{5}{5} - \frac{4}{5} = \frac{1}{5} \]
So, \( \frac{4}{5} \) plus \( \frac{1}{5} \) equals 1 whole. Therefore, the answer is:
\[ \frac{1}{5} \]