求翻译：2、付款方式：培训开始前十个工作日预付合同总金额的50%，培训项目进行到中期前乙方提供发票后五个工作日内支付剩余50%。是什么意思？

2, methods of payment: ten working days before the start of training 50% of the total amount of the prepaid contract, training projects to the medium-term provision within five working days of the invoice before payment of the remaining 50%.