Mdas Calculator Online
Candi Ruman
Nobody actually understood the first part about using a basic calculator. I initially thought the challenge was all about the rules of maths.And when I asked why nobody else applied the rules of maths, they all forgot about it, not because the challenge said to use some "basic calculation"
My original question, on Maths Stack (this one) was why MENSA used 30 instead of 31.5. And initially I did not understand that using a basic calculator meant calculating left to right by pressing equals after each operation.
So what is going on here? If they wanted us the ignore rules of math they should of said taht. Because my basic calculator gives me 31.5 and not 30.0 (I dont have a special. Casio MENSA calculator though)
Why was I the only one that applied the rules of maths on this? ANd when I asked why nobody else applied the rule of maths, I got the weirdest looks. Nobody knew about multiplication before division, subtraction before adding? I thought that was why the question was marked as the most difficutl to test if you knew this.
Sadly, many people forget the basic rules of arithmetic as they (a) don't view them as affecting their lives, (b) didn't like maths, and/or (c) know technology can handle the problem for them. The issue with the last point is that different technologies handle things differently. The Google calculator (much like most graphing calculators) will handle order of operations for you correctly. The standard Windows calculator appears to be operating like an old 4 function calculator which evaluates after every operation is completed as opposed to correct order of operations. Though this can also happen when users hit enter after every operation is finished as opposed to when the whole expression is finished. (Don't have access to a Windows calculator right now so can't tell which is the reason for the wrong answer.)
However, multiplication and division have the same precedence, as does addition and subtraction. When multiplication and division (or addition and subtraction) are both part of an expression, we evaluate which ever appears first (when reading from left to right).
Effectively, such calculators thus evaluated all expressions stricly from left to right, ignoring arithmetic precedence; the sequence of button presses 5 ? 4 ? 7 ? 3 ? 2 = would be evaluated as (((5 ? 4) ? 7) ? 3) ? 2 = regardless of the operators the ? marks stood for.
There is a difference between IQ and simply knowing rules. Figuring out how to get to 30 takes a keen eye and a bit of thought (calculators not allowed for MENSA test). e.g. imagine this a multiple choice question without the answer 31.5.
The question setters are trying too hard. It's the case that you need to be able to think like them to get the right answer rather than being intelligent. If they meant that the calculator ignores rules of precedence then they should state that explicitly as a basic calculator can mean many things and doesn't have to exclude rules of precedence as computing is very cheap compared to the 80's when a basic calculator might be expected to ignore precedence.
So then, you want to multiply the two biggest numbers you can and have the largest denominator as possible when subtracting or smallest denominator as possible when adding. You could do an proof by exhaustion since the dataset is small:
But parentheses weren't allowed in the original question so you cannot apply them selectively. You either work with mdas rules (implied parentheses) or the primitive left to right calc. Thus neither 61.5 nor 63 are valid.
the answer is 31.5. you know it but you messed up the math.with subtraction and addition it shouldnt matter which is carried out first; they can both be considered to be identical functions (addition of a positive and a negative no or vice versa)
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