\documentclass[a4paper,10pt]{article} \usepackage[utf8]{inputenc} %opening \title{} \author{} \begin{document} \maketitle \begin{abstract} \end{abstract} \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. \end{document}