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Here is a really dumb question, but I cannot find answers on Google for some reason or other. All the answers seem to be buried under mounds of percent difference formulas (which is not what I am asking).

I am trying to generate a value between two variables based on a percentage.

$$\begin{align*} 0\% &= X \qquad \text{(the minimum value)}\\\\ 50\% &= \frac{X + Y}{2}\\\\ 100\% &= Y\qquad \text{(the maximum value)} \end{align*}$$

What would the formula be?

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Readers, it might be useful to know that this is essentially the lerp() function, which stands for linear interpolation. I figured this out after a little under a month that I posted. –  Stop forgetting my accounts... Sep 2 '13 at 7:57
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2 Answers

up vote 1 down vote accepted

$$X+(\text{percent here})\cdot(Y-X)$$ So for example,

$X+(25\%)\cdot(Y-X)$ is $25$ percent of the way to $Y$, from $X$.

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The formula for "$t$ percent", where $t$ is any number between $0$ and $100$, is $$\left(1-\frac{t}{100}\right)X+\left(\frac{t}{100}\right)Y$$

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