Uncle Zhang bought a pair of sneakers with a price tag of 400 yuan in the mall. When he bought it, the mall was holding an event. The sneakers were 20% off and the cash back was 40 yuan for purchases over 300 yuan. How much discount did Uncle Zhang buy for this pair of shoes?
张叔叔在商场买了一双标价400元的运动鞋，购买时商场正好搞活动，该运动鞋打八折并且购物满300元返还现金40元．张叔叔买的这双鞋实际打了几折？
<result>7</result>