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So I came across a picture on facebook with a simple math problem. Some of the answers to it were 60, 65, 15 (alot fought this) and some thought like me, 25. This is the picture.

So how I solved it was that I present Soda as: $X$, Burger as: $Y$ and Fries as: $Z$ and than solved it as a set of linear equations.

$$ \left[ \begin{array}{ccc|c} 3&0&0&30\\ 1&2&0&20\\ 0&1&2&9 \end{array} \right] \left[ \begin{array}{ccc|c} 1&0&0&10\\ 1&2&0&20\\ 0&1&2&9 \end{array} \right] ... \left[ \begin{array}{ccc|c} 1&0&0&10\\ 0&1&0&5\\ 0&0&1&2 \end{array} \right]$$

Than just insert the value of $X$, $Y$ and $Z$ in the equation at the bottom. $$5 + (2 * 10) = 25$$ This have to be correct, otherwise I Really have to rehearse my linear algebra.. The reason I ask here is just that So many people are certain that the value is 15 for some reason.

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1 Answer

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It is actually 15. Notice that there is only 1 fry container in the last row.

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