If you have X amount of money and Y goods/service, the ratio of money per unit of good/service is X/Y. Economic growth increases the amount of goods/services pr

If you have X amount of money and Y goods/service, the ratio of money per unit of good/service is X/Y. Economic growth increases the amount of goods/services provided; tractors dig more holes than shovels, and so on. This means Y increases, and thus X/Y must decrease: the cost per unit of good/service decreases.