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Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion


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October 27th, 2017, 05:14 PM   #1
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Increase and decrease with percentages with everything an integer

Maybe this is impossible? I thought this would be easy but spent a few hours on it already, or maybe I'm just too stupid...

I need to take an integer (let's say 124), multiply(/increase) it by a percentage (300% or greater) that will definitely be an integer (easy), and then - divide(/decrease) it by 2 percentage values (percentages that are also integers), keeping both result values integers, and arrive back at the original number again. I can make sure the original numbers are even (or odd) but can't really change them too much beyond that. I can also divide by more than 2 percentages, if that's necessary, but not less.

I should be very specific, when I say divide by percentage, I guess I specifically mean multiply by a percentage lower than 100%, as to have the effect of division. Is this mathematically possible and can you help me with a formula? Something like:-

124 x 300% = 372
372 x X% x Y% = 124
X Y = ?

(PS - this is not homework or something like that, it's a programming thing and I'm not a programmer :P)
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October 27th, 2017, 08:16 PM   #2
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124 × 400% = 496
496 × 50% × 50% = 124

124 × 500% = 620
620 × 50% × 40% = 124

124 × 625% = 775
775 × 80% × 20% = 124

124 × 1250% = 1550
1550 × 40% × 20% = 124
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October 27th, 2017, 08:18 PM   #3
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I forgot to make it much clearer, I need to start with a 300% increase, even if I use a higher value after to divide from (which is what I meant by "300% or greater", I should have said "300% then greater"), which is really the whole problem here - someone suggested 400% and 50% 50%, which seems really too obvious, but then - how to get from 300% to 400%? = 133.333...%
So, that's not going to work either! Whatever the higher percentage is, needs to be done from an original 300% value and also be an integer percentage, if that makes sense. Maybe I'm not so stupid after all, and this is really impossible without dipping into the decimals?
Or maybe there's another value that is close enough to 300% but that is more "friendly" here? 200% and 400% will not work. Something very close to 300% might and still be accurate enough.

Last edited by slothette64; October 27th, 2017 at 08:21 PM.
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October 27th, 2017, 09:24 PM   #4
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If I understand you correctly, the closest one can get to 300% is 320% (which requires the original number to be a multiple of 5), and then you can apply another multiplier, such as 125%.

125 × 320% × 125% = 500
500 × 50% × 50% = 125
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October 28th, 2017, 02:12 AM   #5
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Hmmm, that's pretty good for a lot of the stuff I need to do, but some of the values just can't shift enough to end with 0 or 5 without the accuracy being too far off. I could shift them by 1 and still have just enough accuracy most of the time, but any more and it will be too obvious that it's not programmed correctly. It's a bit hard to explain why, it concerns AI and projectiles and player hit detection. I'm thinking that the whole damn system needs a major rewrite to be tweaked in this way, but I am not qualified enough to do that, obviously.

Thank you for your time, anyway.
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October 31st, 2017, 02:44 AM   #6
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It may be worth telling us what you're actually trying to achieve as there may be a different way to do it.
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