75% of the normal price of headphones is 45$. What's the normal price?
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Answer:
60$ is the normal price.
Why:
Because if 45$ is 75%, then 30$ is 50%, 15 is 25%, and 0 is 0%. 50% + 50% = 100%. (That's how I did this one, anyway. This works on any 25%, 50%, or 75% problem.)