Javascript>

If you are in the data science industry, you would be bothered if you don't have normal distribution table. I came across the article in Stackoverflow that converts z-score to probability in JavaScript. What I really want to know is the **reverse calculation** of this function.

```
/**
* @param {number} z - Number of standard deviations from the mean.
*/
function GetZPercent(z) {
// If z is greater than 6.5 standard deviations from the mean
// the number of significant digits will be outside of a reasonable
// range.
if (z < -6.5)
return 0.0;
if (z > 6.5)
return 1.0;
var factK = 1;
var sum = 0;
var term = 1;
var k = 0;
var loopStop = Math.exp(-23);
while (Math.abs(term) > loopStop) {
term = 0.3989422804 * Math.pow(-1, k) * Math.pow(z, k) / (2 * k + 1) /
Math.pow(2, k) * Math.pow(z, k + 1) / factK;
sum += term;
k++;
factK *= k;
}
sum += 0.5;
return sum;
}
```

I have a sense of how to convert z-score into the probability. But, I have no idea how to calculate the z-score(Standard deviation) from corresponding probability in javascript. For example, If I put in 0.95 (or 95%), I can expect to get 2.25 standard deviation. Above code gives me 95%, if I enter 2.25.

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