Tan will need to meet a margin call for $2,240 when the index falls on 27 August and his margin account dips to $2,760.

• 张三的盘口在8月27日遭受了损失，造成结算后的保证金余额只剩2760元，所以需要补仓。每当补仓时，张三必须再拿出2240元。