Question: The scale of a blueprint of a house is 1 inch : 4 feet. If a room on the blueprint measures 3 inches long, how long is the actual room?
1. **State the problem:** We are given a scale where 1 inch on the blueprint corresponds to 4 feet in real life. We need to find the actual length of a room that measures 3 inches on the blueprint.
2. **Formula and explanation:** The actual length can be found by multiplying the blueprint length by the scale factor.
$$\text{Actual length} = \text{Blueprint length} \times \text{Scale factor}$$
3. **Apply the values:**
$$\text{Actual length} = 3 \text{ inches} \times 4 \text{ feet per inch}$$
4. **Calculate:**
$$\text{Actual length} = 12 \text{ feet}$$
5. **Answer:** The actual room is 12 feet long.