使用百分比查找範圍內的值 (find the value within a range using percent)

問題描述

使用百分比查找範圍內的值 (find the value within a range using percent)

我有一個數字範圍 40 到 255，其中 40 是 0%，255 是 100% 我怎樣才能得到 50% 的數字？

我嘗試搜索尋找一種方法來做到這一點，但找不到任何方法。

參考解法

方法 1:

• You have (255‑40) = 100%
• 1% = (255‑40)/100
• 50% = ((255‑40)/100) * 50 = 107.5
• Since you have offset of 40 at the beginning, 50% from offset = 107.5 + 40 = 147.5

</ul>

方法 2:

Extending @Kiran s answer with some generic Javascript

const rangeMin = 40;
const rangeMax = 255;
const percentage = 50;

const valueFromPercentage = (((rangeMax ‑ rangeMin) / 100) * percentage ) + rangeMin;

const rangeMin = 40;
const rangeMax = 255;
const value = 147;

const percentageFromValue = ((value ‑ rangeMin) / (rangeMax ‑ rangeMin)) * 100;

方法 3:

Any number c in an interval [a, b] can be written as a linear combination of the two endpoints c = a*x + b*(1‑x) for some x ∈ [0, 1].

For [a, b] = [0, 100], the number c = 50 can be written as 0*0.5 + 100*0.5 so x = 0.5.

If the interval [0, 100] is linearly mapped to [40, 255], the ratio x = 0.5 will stay the same, and so c gets mapped to c' = 40*0.5 + 255*0.5 = (40 + 255)/2 = 147.5.

(by usupyusuke、Kiran、Pascal Lamers、dxiv)

參考文件

1. find the value within a range using percent (CC BY‑SA 2.5/3.0/4.0)