How is the zakat on trade goods calculated when the purchase dates of the merchandise differ?

Zakat must be calculated using lunar months, and the start date of the Hijri year (hawl) should be determined. If the five thousand dinars are profit from the shop, they are added to the other merchandise, and zakat is paid on all of it when the hawl is complete. However, if they are from another source, a new hawl begins for them, and it is permissible to pay their zakat in advance along with the other merchandise. The merchandise purchased for ten thousand dinars is subject to zakat if a hawl has passed on its original price.