Suppose you wanted to calculate the percentage of men that weigh inbetween 140 and 170 lbs. This is possible if you carry a few data points such as the average weight of men (mean), the standard deviation, and the specific weight you want to measure (data point).

# Step 0 - Install Normal Distribution Package

The normal distribution package contains a "Standard Normal Distribution" table that will help us with our calculations.

``````npm i normal-distribution --save
``````

# Step 1 - Let's Start Solving

``````'use strict';
const util = require('util');
const NormalDistribution = require("normal-distribution");

// This class will make it easy for us to get the values that are left of the z-score.
class StandardNormalDistTable {
// Provide the Z Table Object
static get zTable(){
return NormalDistribution.default.zTable;
}
// Based on the z-score, provide the chart value
static chartValue(zScore){
let absZScore = Math.abs(zScore);
console.log(absZScore)
let zRow = Math.floor(absZScore * 10) / 10;
//let zCol = ._round((Math.round(absZScore * 100) % 10) / 100, 2);
let zColIndex = (Math.round(absZScore * 100) % 10);
let chartValue = this.zTable[zRow][zColIndex];
return chartValue;
}
}

// Problem #1
// Which percentage of men weigh more than 211 lbs?
// // // // // // // // // // // // // // // // // //
function overWeight(mean, standardDeviation, dataPoint){
// A. First create a normal distribution object.
var normDist = new NormalDistribution.default(mean, standardDeviation)
// B. The zscore will tell you how far you are from the mean.
var zScore = normDist.zScore(dataPoint);
// C. Use the zscore to get the value from the distribution table.
var chartValue = StandardNormalDistTable.chartValue(zScore);
// D. Subscract from 1
let value = Number( (1 - chartValue).toFixed(3) );
// E. We're done.
let solution = util.format('Around %s of men weight more than %s pounds.', value, dataPoint);
console.log( solution);
}
overWeight(150, 25, 211)

// Problem #2
// What is the probability that a man weighs between 170 and 140 lbs
// // // // // // // // // // // // // // // // // //
function inBetween(mean, standardDeviation, lowDataPoint, highDataPoint){
// A. Find the Z Score for the low data point.
var zScore = (lowDataPoint - mean) / standardDeviation;
var chartValue = StandardNormalDistTable.chartValue( zScore );
var valueLow = Number( (1 - chartValue).toFixed(3) );

// B. Find the Z Score for the high data point.
var zScore = (highDataPoint - mean) / standardDeviation;
var chartValue = StandardNormalDistTable.chartValue( zScore );
var valueHigh = Number( chartValue.toFixed(3) );

// C. Subtract the two values to get the center & make it a percentage
var value = Number( (valueHigh - valueLow ).toFixed(3) * 100 );
let solution = util.format('About %s% of the men are between %s and %s pounds.', value, lowDataPoint, highDataPoint);
console.log(solution)
}
inBetween(150, 25, 140, 170)
``````