HP 35s Extract Denominator from Fraction

08112014, 04:43 AM
Post: #1




HP 35s Extract Denominator from Fraction
Hi,
Is there any way to extract the denominator (or numerator) from a fraction on the HP 35s? I'm trying to convert mixed fractions to improper fractions. It's a small thing but if it's possible I would appreciate any help. Thanks in advance 

08112014, 05:29 AM
Post: #2




RE: HP 35s Extract Denominator from Fraction
(08112014 04:43 AM)bcode Wrote: Hi, No, it's not possible, since it's only a display mode, which means that the denominator that's displayed only exists in the display and is not available anywhere for calculations. (If anyone here knows differently, please post the method!) However, here's a trivial trick that sort of "converts" mixed numbers to improper fractions: just press 1/x, and read the result upside down (as it were). Example: leftshift Display: ALL leftshift pi rightshift FDISP > see 3 16/113 1/x > see 113/355 (so the original = 355/113) Thus we have "converted" 3+16/113 into 355/113. Unfortunately, this "trick" occasionally fails for various reasons, like here: 7 sqrt > 2 2295/3554 1/x > 765/2024 (which means 2024/765, but we wanted 9403/3554). What that happens, you have to do it manually, which is easy since the 35s has a twoline display: If a+b/c is displayed, then: Desired Numerator = c*a+b Desired Denominator = c <0ɸ0> Joe 

08112014, 07:37 AM
Post: #3




RE: HP 35s Extract Denominator from Fraction
Oh wow thanks for that tip. And yeah, your example fails because the maximum denominator is 4095, which is understandable.


08112014, 09:06 AM
Post: #4




RE: HP 35s Extract Denominator from Fraction
May I recommend a WP 34S for that application? It features DECOMP doing exactly what you were requesting. And it allows for displaying fractions both in proper and improper form.
d:) 

08112014, 04:14 PM
Post: #5




RE: HP 35s Extract Denominator from Fraction
(08112014 07:37 AM)bcode Wrote: And yeah, your example fails because the maximum denominator is 4095, which is understandable. Exactly. However, sometimes the 1/x trick fails even when the denominator would be 4095 or less, due to roundoff errors, since pressing 1/x doesn't really reciprocate the fraction that's displayed, but instead performs a roundedoff approximation of the reciprocal of a number which itself is already a roundedoff approximation. I just now tried to whip up an example of that, and couldn't find one, but I know I've often seen it in the past, so don't be surprised when it happens. <0ɸ0> Joe 

08122014, 03:08 AM
Post: #6




RE: HP 35s Extract Denominator from Fraction  
08122014, 03:09 AM
Post: #7




RE: HP 35s Extract Denominator from Fraction
(08112014 04:14 PM)Joe Horn Wrote:(08112014 07:37 AM)bcode Wrote: And yeah, your example fails because the maximum denominator is 4095, which is understandable. Ya well it'll be easy to spot since the numerator of the reciprocal should match the denominator of the original. 

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