Popcorn poped

This problem is quite fun, when you look at it:

First, we should find how much money did they make after selling everything, so: $250\times0.5=125$

Now, we can chose one of two paths:

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Path N $1$

We make proportion right away:

$\frac{\$125}{\$112.5}=\frac{100\%}{x\%}$

Let's solve for $x$ :

$x = \frac{112.5\times100}{125}=90$

Careful! We found how much of money they made, not how much they lost!

$100\%-90\%=\boxed{10\%}$

Answer: $\boxed{10\%}$

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Path N $2$

We could try to find the value in dollars, of how much they lost:

$\$125-\$112.5=\$12.5$

Now it's see through what the answer is, but to make sure we could make proportion:

$\frac{\$125}{\$12.5}=\frac{100\%}{x\%}$

Let's solve for $x$ :

$x = \frac{12.5\times100}{125}=\boxed{10}$

Answer: $\boxed{10\%}$

250*0.5=125

125-112.5=12.5

Everybody can notice that 12.5 is 10% of 125.