Discount on old jewelry: the price of the day * 0.88 * the weight of old gold, and the new jewelry must be heavier than the old gold. Make up the difference.

Take gold as an example: if your old gold is 3 grams, today's new gold selling price is 335, the old gold exchange price is 295, and the old gold discount is 3*295=885 yuan.

Ps: The exchange price of platinum is about 20% of the gold price of that day.

If you are not clear, you can ask. ...