To do this, you can first convert the percentage form to its decimal form, like this
![225\text{\%}=(225)/(100)=2.25](https://img.qammunity.org/2023/formulas/mathematics/college/82oty2hkzcptjrvkjq5ia7biebk5x61jdi.png)
Now, you can convert the numbers that are possible answers into their decimal form, like this
Option A.
![2(1)/(4)=(2\cdot8+1)/(4)=(8+1)/(4)=(9)/(4)=2.25](https://img.qammunity.org/2023/formulas/mathematics/college/qhsge97jfm7b4x950d4vwvgh1mn8qa5tdg.png)
Option B.
![(9)/(4)=2.25](https://img.qammunity.org/2023/formulas/mathematics/college/tpx1uyb54g6ai94rcdxzeyszj7mx0va0r3.png)
Option C.
![(50)/(40)=(5\cdot10)/(4\cdot10)=(5)/(4)=1.25](https://img.qammunity.org/2023/formulas/mathematics/college/4xj8z47hwmkwy2ycw5y1sjgdogvtuicydz.png)
Option D.
![(45)/(20)=(9\cdot5)/(4\cdot5)=(9)/(4)=2.25](https://img.qammunity.org/2023/formulas/mathematics/college/ks4vt02cu7rnxhogjt39tpt909249wi42z.png)
Therefore, the number that is not equal to 225% is 50/40 and the correct answer is C. 50/40.