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Mixed Fractions on the HP Prime
01-10-2018, 01:56 AM
Post: #1
Mixed Fractions on the HP Prime
My son is learning how to do arithmetic using mixed fractions. The other night I needed to check his homework. My assumption was that on the HP Prime it would be easy and fast to check a series of mixed fraction addition and subtraction problems. But, I found I could only do this by switching between CAS and HOME, a bit cumbersome. There must be an easier way?

For example: 5 3/4 + 11 7/9 = 17 19/36

My Procedure:
[CAS] 5 + 3/4 + 11 + 7/9 <Enter>
631/36 (a b/c)
17.52777777778
[HOME]
(Menu) 2Get from CAS
17.52777777778 <Enter>
(a b/c)
631/36
(a b/c)
17+19/36 Finally!

Thanks,
Steve
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01-10-2018, 04:04 AM (This post was last modified: 01-10-2018 04:05 AM by Tim Wessman.)
Post: #2
RE: Mixed Fractions on the HP Prime
Just stay in home for all of it and press the [a b/c] key again. It cycles through different representations.

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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01-10-2018, 11:58 AM
Post: #3
RE: Mixed Fractions on the HP Prime
(01-10-2018 04:04 AM)Tim Wessman Wrote:  Just stay in home for all of it and press the [a b/c] key again. It cycles through different representations.

Ah yes. I guess what was throwing me was that I couldn’t do this entirely in the CAS.
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01-11-2018, 02:51 AM
Post: #4
RE: Mixed Fractions on the HP Prime
(01-10-2018 11:58 AM)smartin Wrote:  
(01-10-2018 04:04 AM)Tim Wessman Wrote:  Just stay in home for all of it and press the [a b/c] key again. It cycles through different representations.

Ah yes. I guess what was throwing me was that I couldn’t do this entirely in the CAS.

You can do it entirely in CAS, and it's guaranteed to be correct, unlike the Home method shown above which is NOT guaranteed to be correct, and in fact will ALWAYS be wrong if the fractions have more than a few digits in them, or if you're in FIX 2 mode or similar. Just type propfrac(Ans) and your fraction answer will be converted into the desired mixed number. The first example below is yours. The second example below shows how CAS gets the correct answer, but if you try the Home method it gets it wrong, even in Standard display mode.

[Image: propfrac.png]

Only use the Home [a b/c] method if (1) you're in Standard display mode, and (2) the fraction only has a few digits in it (e.g. very simple homework problems!).

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01-12-2018, 02:50 AM
Post: #5
RE: Mixed Fractions on the HP Prime
(01-11-2018 02:51 AM)Joe Horn Wrote:  
(01-10-2018 11:58 AM)smartin Wrote:  Ah yes. I guess what was throwing me was that I couldn’t do this entirely in the CAS.

You can do it entirely in CAS, and it's guaranteed to be correct, unlike the Home method shown above which is NOT guaranteed to be correct, and in fact will ALWAYS be wrong if the fractions have more than a few digits in them, or if you're in FIX 2 mode or similar. Just type propfrac(Ans) and your fraction answer will be converted into the desired mixed number. The first example below is yours. The second example below shows how CAS gets the correct answer, but if you try the Home method it gets it wrong, even in Standard display mode.

[Image: propfrac.png]

Only use the Home [a b/c] method if (1) you're in Standard display mode, and (2) the fraction only has a few digits in it (e.g. very simple homework problems!).

Thanks for the detailed explanation. I'm now just getting used to, and learning to appreciate, the virtues of having a separate HOME and CAS workspace. But, I do find it a bit unpleasant that this simple use case of mixed fraction arithmetic should require rather specific knowledge of how the two modes behave to get the correct answer. I can't help but imagine how a student might get confused by this. It seems to me an area which could be improved in the OS.
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01-12-2018, 04:09 AM (This post was last modified: 01-12-2018 04:17 AM by Tim Wessman.)
Post: #6
RE: Mixed Fractions on the HP Prime
Did any of the homework problems not work perfectly using the [a b/c] key in home? Joe is a fraction nut and goes into the depths, when this simple use case is exactly what the [a b/c] key does with basically no fuss. Smile

The CAS doesn't handle mixed fractions because mixed fractions are basically useless past the "lets learn about mixed fractions" stage and so there isn't any need or desire to be cycling values containing them.

TW

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01-12-2018, 04:27 AM
Post: #7
RE: Mixed Fractions on the HP Prime
(01-12-2018 04:09 AM)Tim Wessman Wrote:  Did any of the homework problems not work perfectly using the [a b/c] key in home?

Yes: If the Finance app is the current app, then using the [a b/c] key to find a mixed number for Steve's example (5 3/4 + 11 7/9 = 17 19/36) fails. It says it's 17+8/15, which is wrong.

(01-12-2018 04:09 AM)Tim Wessman Wrote:  Joe is a fraction nut and goes into the depths, when this simple use case is exactly what the [a b/c] key does with basically no fuss. Smile

Unless you're in the Finance app. Or if you set a display mode other than Standard. Or if the fraction contains more than a few digits. But only a nut would worry about those things ever happening. Wink

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