Answer:
45% of the tickets were sold in the afternoon
Explanation:
You set the problem up like this:

Then you cross multiply the two, so you multiply the 225 by 100 and the 500 by the ?, which is the % out of 100 that you want to find. That gives you this equation:

Then you just solve for the ? (or whatever variable you want to call it). All you have to do is divide by the 500 to get the ? by itself. That gives you 45%!
If you want a shorter way you can also just take that original equation, divide the 225 by 500 and multiply by 100 to give you 45% as well. Either way works.
Here is the general formula my teacher taught us for percents just in case you want it for the future:

Hope this helps! ☺