JSFiddle - React, Tailwind, and code Playground

HTML

<p id="first"></p>
<p id="operator"></p>
<p id="second"></p>
<p>=</p>
<input id="entry"></input>
<button onclick="calc()">
  Validate
</button>

JavaScript

/* Build some random numbers between 1 and 10 */
var first = Math.floor((Math.random() * 10) + 1);
var second = Math.floor((Math.random() * 10) + 1);
var operator = ['+', '-', '*', '/'];

/* Get a random operator */
var index = Math.floor(Math.random() * 4);
var operator = operator[index];

/* Render HTML */
document.getElementById('first').innerHTML = first;
document.getElementById('operator').innerHTML = operator;
document.getElementById('second').innerHTML = second;

function calc(p1, p2) {
  /* Fetch user input */
  var entry = document.getElementById('entry').value;

  /* Calc result */
  var result = "";
  switch (index) {
    case 0:
      result = first + second;
      break;
    case 1:
      result = first - second;
      break;
    case 2:
      result = first * second;
      break;
    case 3:
      result = first / second;
      break;
  }

  /* Validate result */
  if (entry == Math.round(result * 100) / 100) {
    alert("Richtig!")
  } else {
    alert("Falsch!")
  }

}