JSFiddle - React, Tailwind, and code Playground

JavaScript

function getNumber(probabilities){
    var rnd = Math.random();
    var total = 0;
    var hit;
    for(var i = 0; i < probabilities.length; i++){
      if(rnd > total && rnd < total + probabilities[i][0]){
           hit = probabilities[i]
      }
      total += probabilities[i][0];
    }
    return Number((hit[1] + (Math.random() * (hit[2] - hit[1]))).toFixed(2));
}

var number = getNumber(
  [
    [0.4, 1, 10], 
    [0.2,11,20], 
    [.3,21,30], 
    [.1,31,35]
  ]
);

console.log(number);