1. The problem is to find the proportion of 45 out of 50 and then express it as a percentage of 100. 2. The formula for proportion is $\text{Proportion} = \frac{\text{Part}}{\text{Whole}}$. 3. Here, the part is 45 and the whole is 50, so the proportion is $\frac{45}{50}$. 4. To express this proportion as a percentage of 100, multiply by 100: $$\frac{45}{50} \times 100 = 90$$. 5. Therefore, 45 out of 50 is equivalent to 90 out of 100, or 90%.