If the restaurant sells 3 times as many white potatoes as sweet potatoes, we can set the quantity of sweet potatoes as \( x \) and the quantity of white potatoes as \( 3x \).
To find the ratio of sweet potatoes to white potatoes, we express this as:
\[ \text{Ratio} = \frac{\text{sweets}}{\text{whites}} = \frac{x}{3x} \]
This simplifies to:
\[ \frac{1}{3} \]
Hence, the ratio of sweet potatoes to white potatoes is \( 1 \) to \( 3 \).
The correct answer is:
1 to 3.