Código HTML:
<html>
<head>
<script>
function va(numero){
if(numero >= 0 && numero <= 50){
i=0;
}else if(numero <= 70){
i=1;
}else if(numero <= 80){
i=2;
}else if(numero <= 100){
i=3;
}else if(numero <= 115){
i=4;
}
document.form.valor[i].checked = true;
}
</script>
</head>
<body>
<form name="form">
<input type="text" name="numero" id="numero" onkeydown="va(this.value);" onkeyup="va(this.value);">
<input type="radio" name="valor" value="0" />
<input type="radio" name="valor" value="1" />
<input type="radio" name="valor" value="2" />
<input type="radio" name="valor" value="3" />
<input type="radio" name="valor" value="4" />
</form>
</body>
</html>