As Terry mentioned, I divided the problem as half of 500, and half of 50.
That's how I did it, too.
The curious thing is, I have read that this is what they are supposed to be teaching in schools today. That's the easy way to do it in your head, but on paper I think the traditional way is better/easier/faster. On the other hand, in today's "everyone gets a trophy" world, where requiring answers to be
correct is racist and discriminatory, I believe teachers are also supposed to grade based on the method rather than the end result. So if a student's method was to take a number, divide it by two, and the result was any number smaller than the original number ==? PASS.