To find the missing number in the equation \( 79.00 \times x = 7.90 \), we can isolate \( x \) by dividing both sides of the equation by \( 79.00 \):
\[ x = \frac{7.90}{79.00} \]
Next, we can perform the division:
\[ x = \frac{7.90}{79.00} = 0.1 \]
Therefore, the missing number is
\[ \boxed{0.1} \]