3 caculators = 3 different answers to one math problem

1 ambiguous notation, 3 different interpretations. The Casios both have reasonable interpretations, but the iPhone should probably give some kind of warning that it is about to ignore entire numbers.

Math PhD student here. The issue is that people are confusing two symbols which are distinct: the solidus (/) and the obelus (÷). The latter is rather obsolete and it's not clear why exactly calculators use it. Anyway, this blog post clears up the issue better than I could hope to in a comment: <a href="http://www.matthewcompher.com/posts/trouble-with-semantics-the-obelus-or-division-symbol-%C3%B7/" rel="nofollow">http://www.matthewcompher.com/posts/trouble-with-semantics-t...</a>

Mentally, I perform no-written-operator multiplication first, then anything else, so I can see why the calculators (and WolframAlpha, in some cases) are getting the intention wrong:<p>"6 ÷ 2x" gets parsed as "6 / (2 * x)"<p>"6 ÷ 2 * x" gets parsed as "(6 / 2) * x"<p>All that's done in the equation in the article is having a pair of brackets instead of a variable, but the result is the same to my brain.

RPN (Reverse Polish Notation) gets things done on a calculator. This article shows one reason why it's not just for finance.

I enjoyed the bit at the end where the writer managed to use the wrong (IMO) formula to arrive at the correct answer.<p>Using BEDMAS as I was taught, so many moons ago:<p>6 ÷ 2 ( 1 + 2 )<p>6 ÷ 2 ( 3 )<p>6 ÷ 2 * 3 // because 2(3) is not an exponent or algebraic construct, it's straight multiplication<p>3 * 3 // division and multiplication are in left-to-right order, no precedence<p>9

In Microsoft Excel we get:<p>"Microsoft Excel found an error in your formula you entered. Do you want to accept the correction proposed below?"<p>=6/2*(1+2)<p>Which then gives 9.

Hm, Calcbot on the iPhone also returns 2 if entered without a multiplication after the first "2". Hitting the open parenthesis key removes the "2" from the calculation. Since Calcbot displays what you've entered below the answer, it's easy to see the mistake with a trivial calculation like this, but if you're not watching for it it's easy to miss. Better than the built-in calculator and PCalc, which provide no feedback and give the wrong answer, but surprising.

OK, I get the first two. Strictly speaking, mult and div have the same precedence (6 / 2 * 3 should be the same as 6 * 3 / 2 , both 9), but in one case, the calculator interpreted the multiplication in 2(1+2) as having higher precedence than 2*(1+2). Arguably a bug, but nothing crazy.<p>But ... the iPhone gives 2? I don't get it.<p>(FWIW, Android says 9)

when i was a kid, i was told to use the BODMAS rule i.e Brackets, Orders, Division or Multiply, Addition or Substraction<p>After you have done "B" and "O", just go from left to right doing any "D" or "M" as you find them.<p>Then go from left to right doing any "A" or "S" as you find them.

Multiplication and division have the same precedence, so you do them left-to-right as written. Like addition and substitution.<p>Or better yet, realise that writing it all on one line is stupid and ambiguous, and write properly.

to me, elided multiplication has a higher precedence than the explicit one (and by transitivity, than the explicit division), but I don't remember in which grammar I read that (mathematica, matlab ?).

In WolframAlpha 6÷2(1+2) gives 9 but 6÷2x with x=(1+2) gives 1.

I would have expected an answer of 3 as 2(1+2) cannot mean anything else than applying the constant function 2 to the sum.

Anyone have a guess to how the iPhone calculator computed 2?

...about time we start teaching prefix notation on schools.

I'm happy to say my mental math and my phone's (Nexus S) math get 9.