How do I convert units if I don't know how many such and such is in such and such?

This is a really basic question.. I have a math problem where I first need to convert miles to meters to actually do the math problem. These kind of math problems always defeat me because I never know how many units of something are in something else. So my math problem showed how to do it and so they said there... show more This is a really basic question.. I have a math problem where I first need to convert miles to meters to actually do the math problem. These kind of math problems always defeat me because I never know how many units of something are in something else. So my math problem showed how to do it and so they said there are 1609 meters/mile. But I didn't know that. Do I have to just remember these conversions in order to do these kind of problems? Am I supposed to automatically know there are 1609 meters per mile? Or is there an actual way to find that out math wise?
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