To determine the scale factor of Ann's drawing, we need to compare the dimensions in the drawing to the actual dimensions.
- The length of the driveway in the drawing is 1 inch.
- The actual length of the driveway is 20 feet.
First, we need to convert the actual length from feet to inches since the drawing's measurement is in inches. There are 12 inches in a foot, so:
\[ 20 \text{ feet} \times 12 \text{ inches/foot} = 240 \text{ inches} \]
Now we can express the scale factor as the ratio of the drawing length to the actual length:
\[ \text{Scale factor} = \frac{\text{Length in drawing}}{\text{Actual length}} = \frac{1 \text{ inch}}{240 \text{ inches}} \]
Next, we simplify the fraction:
\[ \frac{1}{240} \]
The scale factor of the drawing is:
\[ \boxed{\frac{1}{240}} \]