To do this, you can first convert the percentage form to its decimal form, like this
[tex]225\text{\%}=\frac{225}{100}=2.25[/tex]
Now, you can convert the numbers that are possible answers into their decimal form, like this
Option A.
[tex]2\frac{1}{4}=\frac{2\cdot8+1}{4}=\frac{8+1}{4}=\frac{9}{4}=2.25[/tex]
Option B.
[tex]\frac{9}{4}=2.25[/tex]
Option C.
[tex]\frac{50}{40}=\frac{5\cdot10}{4\cdot10}=\frac{5}{4}=1.25[/tex]
Option D.
[tex]\frac{45}{20}=\frac{9\cdot5}{4\cdot5}=\frac{9}{4}=2.25[/tex]
Therefore, the number that is not equal to 225% is 50/40 and the correct answer is C. 50/40.
