[w46823]

<ul>
<li><a onclick="apple.a()">10 Яблочек</a></li>
<li><a onclick="cherry.a()">50 Вишенек</a></li>
</ul>
Вкусняшка <div id="fruitname"></div><br>
Сколько <input id="fruithowmany"  type="text" onmousedown="this.value=this.value.replace(/([^0-9])/g,'');" onkeyup="var n=this.value.replace(/([^0-9])/g,''); if(n!=this.value) this.value=n;" onchange="changed(this);" maxlength="3" size="1" ><br>
Цена <input type="text" id="price"><br>
<div id="fruitsum"></div>

var apple = {fruitName: 'Яблочки', howMany:10, price:4.21};
var cherry = {fruitName:'Вишенки', howMany:50, price:4.32};

function addel() {
   document.getElementById('fruitname').innerHTML = this.fruitName;
   document.getElementById('fruithowmany').value = this.howMany;
   document.getElementById('fruitprice').value = this.price;
   document.getElementById('fruitsum').innerHTML = Math.round(this.price*this.howMany*70)/100; //Замена toFixed(2)
   alert('Остальных 30% ворует правительство!');
}
apple.a = addel;
cherry.a = addel;

var fruithowmanyElem = document.getElementById('fruithowmany');
     fruithowmanyElem.onkeypress = calc;
     fruithowmanyElem.onkeyup = calc;
     fruithowmanyElem.oninput = calc;
     fruithowmanyElem.onpropertychange = function(){
           event.propertyName == "value" && calc();
     };
var fruitpriceElem = document.getElementById('fruitprice');
     fruitpriceElem.onkeypress = calc;
     fruitpriceElem.onkeyup = calc;
     fruitpriceElem.oninput = calc;
     fruitpriceElem.onpropertychange = function(){
           event.propertyName == "value" && calc();
     };

function calc(){
    var skolko = +fruithowmanyElem.value;
    var cena = +fruitpriceElem.value;
    var sum;
        sum = Math.round(cena*skolko*70)/100;
    var otkat = sum*0.3/cena;
    alert('Откат правительству составил '+otkat+this.fruitname);
}