A shopping mall sets a price for a product after adding 50% of the purchase price, and then writes "reward". Selling at 80% of the price, the result is still a profit of 20 yuan per item. How much is the purchase price of this commodity?
某商场将一种商品按进价的50%加价后定价，然后写上"酬宾"．按定价的80%出售，结果每件商品仍获利20元．这种商品的进价是多少元？
<result>100</result>