To find the scale factor used to create the printed photo of the sandbox, we start by comparing the original dimensions of the sandbox to the dimensions in the printed photo.
The original sandbox is a regular hexagon with each side measuring 40 inches. The printed photo depicts the same hexagon but with each side measuring 4 inches.
To find the scale factor, we can use the formula for scale factor:
\[ \text{Scale Factor} = \frac{\text{Length in Photo}}{\text{Original Length}} \]
Substituting the given values:
\[ \text{Scale Factor} = \frac{4 \text{ inches}}{40 \text{ inches}} = \frac{4}{40} = \frac{1}{10} \]
To express this as a decimal:
\[ \frac{1}{10} = 0.1 \]
Thus, the scale factor used to create the printed photo of the sandbox is
\[ \boxed{0.1} \]