一个BPP F3 十四章 control accounts 里的 问题

BPP版 F3 315页的问题
Question中
（i）Discounts received of $50 had been debited to Bell's receivables ledger account.
为什么调整的时候只是减了一个50
在（h）中cash received of $250 had been debited to a personal account.
就减了两倍的250
这两个有啥区别
请高人指点一下
先谢谢啦