All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, may Allaah reward you for being keen on fulfilling what Allaah has prescribed upon you concerning the rights of the poor and the needy in your property. As regards the Zakaah which you have to pay, you should know the value of the tradable items at the end of the lunar year from the time you started running your business if it reached the Nisaab (the minimum amount liable for Zakaah, which is the value of 85 grams of pure gold). So, you should evaluate it according to its market price on the day you want to pay Zakaah and then pay 2.5 percent from it and on any profit made.
As regards the Sum of 47,000 Dirhams, you should pay Zakaah on it at the end of a whole lunar year from the time it reached the Nisaab. In brief, you should pay 2.5% on the total sum which you have when a whole lunar year elapses.
Please refer to Fataawa: 81443 and 82219.
Allaah knows best.