JSFiddle - React, Tailwind, and code Playground

HTML

Bets: <span id="num_bets">300</span>
<br>
Your money: <span id="money">£25.00</span>
<br>
<br>
Bet: <input id="bet" type="number" /> pence

JavaScript

var money = 2500;
var bets = 300;

document.getElementById("bet").addEventListener("keydown", function(e) {
    if (e.keyCode == 13) {
        var bet_amt = parseInt(bet.value);
        if (bet_amt > money || !bets) {
            return;
        }

        if (Math.random() < 0.6) {
            money += bet_amt;
        } else {
            money -= bet_amt;
        }

        document.getElementById("money").innerText = "£" + (money / 100).toFixed(2);
        document.getElementById("num_bets").innerText = --bets;
    }
}, false);