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\section{McDonalds maths puzzle etc.}

Where $D$ is a drink, $B$ is a burger and $F$ is fries:

$$ D + D + D = 30 $$
so $D$ == 10
$$ D + B + B = 20 $$
so $B$ == 5
$$ B + FF + FF = 9 $$
so $FF + FF = 4$ therefore $FF=2$ so $F=\pm \sqrt{2}$

Onto the final equation
$$B + F \times D = \; ? $$

As $F$ is  $\pm \sqrt{2}$ 

there are two valid answers

$ 5 + \sqrt{2} \times 10 $ and $ 5 - \sqrt{2} \times 10 $

So the answer is either 19.142 or -9.142.


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