divideで割り切れる[min, max]のランダムな数を取得

getRandomFlattenNum.js

function getRandomFlattenNum(min, max, divide) {
  let n = Math.random() * (max - min) + min;
  n = flattenNum(n, divide);
  return n;
}

function flattenNum(n, d) {
  return n = n - (n % d);
}