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CG50 Error?


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#1 marshman

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Posted 09 October 2019 - 10:01 AM

Hi all

This is my first post, so forgive any errors. Firstly I am NOT a mathematician; I just bought the above calculator (new) after reading different reviews, as a machine that would help me learn basic arithmetic and anything else I’m likely to need. 

I started doing a list of simple combinations of the basic operators. I tried to work these out myself and then use the calculator to confirm or deny my result. It was some time in, and after huge amounts of frustration, that I realized the calculator was occasionally giving the WRONG result!? What I mean by this is that it gave  a different result to other calculators? 
My question is, is the calculator faulty, or is there another reason? I’m going to try and attach a pic of an example, the result of which, according to several other calculators, is -421

Okay, can’t find how to attach pic of calculator result, so here’s the sum followed by the given result. 
 

11+-3/2(4^2*9)*2

10.97916667

 

Any help very much appreciated!



#2 3298

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Posted 09 October 2019 - 05:18 PM

What key did you use to type 3/2? If it was the regular division key ÷, then the calculator is right (given what the user's guide says about the order of operations when implicit multiplication is involved: in Casio calculators it has higher priority than division). Further reading on the notational issue here.
There are two ways to avoid this pitfall:
- Use explicit multiplication to multiply 3/2 with the parentheses, which has a low enough priority for the division to be calculated first.
- Use the key labeled "a b/c" instead, which turns the whole expression 3/2 into a single number (a fraction) which can be implicitly multiplied with the parentheses without needing to worry about priorities.

Or ... do what I do: use a calculator with reverse polish notation (RPN, you'll see this abbreviation mentioned in the thread I linked), which avoids the issue altogether by shifting the responsibility of navigating priorities into the user's brain. ;) Casio doesn't make RPN calculators though, so that would be an expensive solution, and RPN isn't exactly easy to learn.

#3 marshman

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Posted 10 October 2019 - 04:50 PM

Hi CasioAddict
Very many thanks for taking pity on a poor beginner! Your answer, and the link you provided, were extremely useful even if confusing. I didn’t reply last night because I was packing up for my return from holiday in Wales. I drove back today and haven’t had a chance to fully digest your post, which I’ll study more carefully tomorrow. But, as I was on holiday the only other calculators I could use were iOS apps on my iPad, all of which gave the -421 answer. However, since getting home I’ve tested a couple of other calcs and nearly all of them gave the 10.9 answer. The only exception being my HP 39gll which automatically converted my division input to a fraction and gave the -421 answer! I’ll just mention here that I do have a RPN calculator (an old HP 32s) but it would take me a while to get back into it, having never totally mastered it in the first place!
Will be back after I’ve fully (?) read up about this, because at the moment I’m still confused!

#4 piu58

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Posted 11 October 2019 - 05:30 AM

If I put in the formula in my CG20 it automatically sets more parenthesis. It comes to

11+3/(2(4²*9))*2 (which gives 11,02)

 

The mathematical noted multiplication (without asteriks) has a very high priority, may be the highest at all. If you don't want this set an asteriks:
11+3/2*(4²*9)*2 which gives 443.


Edited by piu58, 11 October 2019 - 05:30 AM.


#5 marshman

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Posted 11 October 2019 - 11:54 AM

Hi Casio Freak
Thanks for your input. Yes, the CG50 adds the extra parentheses also. What you inadvertently missed here was the minus sign after the plus sign; I could have made it clearer by putting the minus three in parentheses I suppose, although it doesn’t make any difference to the calculation.
I’m going to do a bit more study on the HP Museum link that CasioAddict gave, and then perhaps continue the conversation later. But on a quick perusal last night, it would seem this discussion has been going on for some already, and I just came upon it by accident. I’d like to say that although I have a lot of calculators, I’m not an expert at using them!




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