1. Identify the current weight of the dog: 36 pounds.
2. Determine the percentage increase in weight: 20% or 0.2.
3. Use the formula for the original weight:
\text{Original Weight} = \frac{36}{1 + 0.2}
4. Calculate the denominator:
1 + 0.2 = 1.2
5. Calculate the original weight:
\text{Original Weight} = \frac{36}{1.2}
6. Perform the division:
\text{Original Weight} = 30
Therefore, the dog weighed 30 pounds three months ago.