Matt H. answered • 03/26/15
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PATIENT :-) Elem/Middle MATH and WRITING; HS SAT and COLLEGE ESSAYS!
The 100 team is correct.
Do the parentheses first, so it becomes 20 ÷ 2 x 10.
Division and multiplication are in the same pairing, so you go left to right. Even though the acronym PEMDAS seems to say that you would always do the multiplication first, it actually means "do all multiplication and/or division before you do any addition and/or subtraction."
I hope that makes sense. :-)
Matt in NY
Matt H.
ha, so true! I interpreted it the first way you illustrated, but I guess without any spaces between the numbers and signs, we should probably assume that your ultimate explanation is better. The ironic thing as that these purposely tricky PEMDAS riddles really don't serve much practical educational purpose. Oh well, they're fun to explore. Sort of... :-)
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03/26/15
Philip P.
tutor
You're exactly right, Matt. These sorts of problems are intentionally ambiguous, which is a good reason teach kids to use parentheses to remove all ambiguities.
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03/26/15
Michael W.
Well, yes, it's intentionally ambiguous, which is a good reason to use parentheses to remove ambiguity. Even worse, PEMDAS implies that multiplication comes before division, which it doesn't. Multiplication and division are performed left to right in
whichever order they appear, before addition any of the addition or subtraction, as Matt said.
In case we were doing this by democratic vote, my answer is 100, for the record. :) If we're looking for a "definitive" answer, anyone think to try it on their calculator? Type in 20/2(10) and see what you get. Mine says 100. If yours says something
different, then I quit. :)
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03/26/15
Philip P.
03/26/15