Paco had 28 cookies. He ate some of them and had 7 cookies left. How many cookies did Paco eat?
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We know that Paco had 28 cookies to start with. 

We know that he ate some of them, which means that the number of cookies he had left is less than 28. 

We know that he had 7 cookies left, which means that the number of cookies he ate is more than 7. 

So, we can say that Paco ate more than 7 cookies and less than 28 cookies.