To find the area of the entire farm on the scale drawing, we can use the formula for the area of a rectangle:
\[ \text{Area} = \text{length} \times \text{width} \]
Given the dimensions of the farm are 50 cm by 20 cm:
\[ \text{Area of the farm} = 50 , \text{cm} \times 20 , \text{cm} = 1000 , \text{cm}^2 \]
Next, we need the area of the greenhouse, which has dimensions of 25 cm by 10 cm:
\[ \text{Area of the greenhouse} = 25 , \text{cm} \times 10 , \text{cm} = 250 , \text{cm}^2 \]
Now, to find the percent of the farm that is occupied by the greenhouse, we can use the formula:
\[ \text{Percentage} = \left( \frac{\text{Area of the greenhouse}}{\text{Area of the farm}} \right) \times 100 \]
Substituting the values we've calculated:
\[ \text{Percentage} = \left( \frac{250 , \text{cm}^2}{1000 , \text{cm}^2} \right) \times 100 = 25% \]
Thus, the greenhouse occupies 25% of the farm.