1. The problem is to calculate $7\tfrac{1}{2} - 20\%$. 2. Convert $7\tfrac{1}{2}$ to an improper fraction or decimal. $7\tfrac{1}{2} = 7 + \frac{1}{2} = 7.5$. 3. Convert $20\%$ to decimal form. $20\% = \frac{20}{100} = 0.2$. 4. Perform the subtraction: $7.5 - 0.2 = 7.3$. 5. The final answer is $7.3$.