If one quarter (25 cents) is 25% of a dollar, what percent is 23 cents?

You need to apply the same reasoning.

25 cents is 25% of a dollar because they are 25 out of 100, that is 25/100 = 25%

For 23 cents is exactly the same reasoning:

23 cents is 23% of a dollar because they are 23 out of 100 cents, that is 23/100 = 23%