When it comes to order of operations (PEMDAS, BODMAS, BEDMAS, BIDMAS), who are you going to believe: your primary school teacher, or Richard Feynman? Applying PEMDAS to the viral maths puzzle "6/2(1+2) = ?" gives the answer 9, as explained in videos by MindYourDecisions and others, but is that the whole story... I'm an online maths tutor. Go to http://thawom.com/tutoring to find out more. You can also follow me on twitter at https://twitter.com/thawom0 References: Abstract Algebra- The Basic Graduate Year by Robert B. Ash https://faculty.math.illinois.edu/~r-ash/Algebra/SolutionsChap1-5.pdf p2 The Feynman Lectures on Physics Vol. I Ch. 6: Probability http://www.feynmanlectures.caltech.edu/I_06.html Basics of Mechanical Engineering by Paul D. Ronney http://ronney.usc.edu/ame101/ame101-lecturenotes.pdf p7 (page 15 of the pdf) Oliver Knill - Ambiguous PEMDAS http://www.math.harvard.edu/~knill/pedagogy/ambiguity/index.html AMS Guide for Reviewers May 2000 https://web.archive.org/web/20000815202937/http://www.ams.org/authors/guide-reviewers.html APS Physical Review Style and Notation Guide https://cdn.journals.aps.org/files/styleguide-pr.pdf p21