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Hi I have problem with finding right "formula" (Is it what it is called) I am bad at maths so forgive me.

So problem is this. I can insert some number and then it calculates me answer with this "unknown formula". There are what I have. (Let's say that $F$ is "formula")

$$1F=1$$

$$2F=2$$

$$25F=25$$

$$600F=2825$$

$$1000F=4825$$

$$1100F=5325$$

$$1200F=5825$$

$$2500F=12325$$

$$5000F=24825$$

So I can't understand what logic or formula makes those numbers become those answers. If somebody can help or need more numbers, then I can provide them :I

Yuriy S
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Reman
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  • I think you are trying to define your $F$ as a function $F(x)$, then you should write (for example), $F(600)=2825$ - do I understand correctly what you mean? – Yuriy S Jul 03 '16 at 21:30
  • To format math equations surround them with $ symbols. For display format use $$ on each side – Yuriy S Jul 03 '16 at 21:34
  • Related: http://math.stackexchange.com/questions/1790642/general-formula-for-the-1-5-19-65-211-sequence – Jack D'Aurizio Jul 03 '16 at 21:42
  • Sorry guys I am just bad in maths as english so wrong tags. But Jack seems be on right tracks. I just can't resolve this myself. :I – Reman Jul 03 '16 at 21:44
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    @YuriyS: Not that OP is likely aware of this, but the notation "$xf$" to mean what you write as "$f(x)$" is not unheard of, especially in algebra. I don't care for that notation, but I would say this question is pretty good evidence that it is intuitively justified. For analysts, your notation is by far much more standard, and I admit I prefer it. Just saying... – MPW Jul 03 '16 at 21:44
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    Honestly it just looks like if $x < 35$ then $f(x) = x$, and if $x\geq35$, then $f(x) = 5x-175$. But this is assuming $f$ is supposed to be a function. – Rellek Jul 03 '16 at 21:45

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Your last six data points follow the formula

\begin{equation} F(x)=5x-175 \end{equation}

This means multiply the first number times $5$ and subtract 175 to get the second number.

However your first three data points follow a different formula

\begin{equation} F(x)=x \end{equation}

A continuous answer would be

\begin{equation} F(x)=\begin{cases} x \text{ for } x<25\\ 2x-25 \text{ for } 25\le x<50\\ 5x-175\text{ for } x\ge50 \end{cases} \end{equation}

John Wayland Bales
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    ...then, pragmatically, $F(x) = \max(x, 5x-175)$? – Joffan Jul 03 '16 at 21:52
  • @Rellek Your comment was not showing on my screen when I posted my answer. But I am curious where you got the $35$. Oh, nevermind, I see, $175\div5$. – John Wayland Bales Jul 03 '16 at 21:52
  • Hi, your formula works with six last numbers, but when I use number 90 and 100 I got: 90 = 275 and 100 = 325 – Reman Jul 03 '16 at 21:53
  • Look at @Joffan comment. That is the best answer. – John Wayland Bales Jul 03 '16 at 21:55
  • Are 275 and 325 the wrong results for 90 and 100? Explain. – John Wayland Bales Jul 03 '16 at 21:58
  • No they are right. I just didn't first understand... I think this is solved. Thank you all, you're just amazing! :) – Reman Jul 03 '16 at 22:00
  • I added an additional amount to my answer which gives a graph which is continuous. – John Wayland Bales Jul 03 '16 at 22:05
  • @Reman, if you think your question is answered, you can click the checkmark at the top of this post to accept the answer. It will give reputation points to you and the person who answered you – Yuriy S Jul 03 '16 at 22:07
  • Does it mean that numbers after 35 is not equal as base number eg. 34 is 34 but 36 is 36x5-175? Also do I must mark this solved, if must then how I can do it? :o – Reman Jul 03 '16 at 22:08
  • @ Yuriy S, Thanks I will mark it soon. Strangely though when I insert number 34 it becomes 43 and 36 becomes 47 so 34=43 and 36=47. And more... 25=25 and 26=27. Can there be some logic? :o – Reman Jul 03 '16 at 22:13
  • @ Yuriy S, I'm sorry! I mean same as before so $$40F=55$$ and $$ 50F=75$$ – Reman Jul 03 '16 at 22:24
  • @Reman I corrected the value of $x$ where the two functions meet. It is $43.75$ not $35$. – John Wayland Bales Jul 03 '16 at 22:25
  • Okay, here are some more values $$25F=25$$ $$26F=27$$ $$34F=43$$ $$36F=47$$ $$40F=55$$ and $$50F=75$$ – Reman Jul 03 '16 at 22:33
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    Your additional values of $(34,43), (40,55)$ and $(50,75)$ follow a third rule of $F(x)=2x-25$ so there is more going on here than meets the eye. Where are you getting these numbers? – John Wayland Bales Jul 03 '16 at 22:34
  • I am messed up in "programming". I must find what value will become $200$ with following same formula with these other numbers. Formula is hidden in not accesable file and I try manipulate one value in code and build it to see result. :o – Reman Jul 03 '16 at 22:38
  • I modified my answer to incorporate the additional information which you provided. – John Wayland Bales Jul 03 '16 at 22:43
  • Okay! After all calculations I can confirm this is solved! Many thanks for all of you! @JohnWaylandBales, Indeed it gives so $$75x5-175=200$$ – Reman Jul 03 '16 at 22:47
  • The number 75 should give you 200. – John Wayland Bales Jul 03 '16 at 22:48