His buying actually closed the position he sold. Futures are two-way. You can sell them first and then close your position through repurchase.

That is, he sold at 13000 and bought at 10000.

After selling, every futures, corresponding to the index fluctuation, every time the index falls by one point, he will earn 50 yuan, and of course, every time the index rises by one point, he will lose 50 yuan.

From 13000 to 10000, the index * * * fell by 3000 points, and each futures contract earned 15000. He sold three copies, so he earned 450 thousand pounds.