Answer: 1inch : 10 feet
Explanation:
Since we are informed that Mathew builds a model of a house that is 2 in tall, 6 in wide, and 3 in long while the real house is 20 ft tall, 60 ft wide and 30ft tall.
For the length, we can see that the relay house is (30/3) = 10 times the model. The same thing is applicable to others as well as the width and height is 10× the scale used. Therefore, the scale used to build the house is 1inch:10 feet