Find a mathematical formula: If you buy 500 shares with 30 yuan and the share price drops to 28.25 yuan, how many more shares do you need to buy, so the cost is exactly 29.07 yuan?
30*500 + 28.25*X = 29.07*(500+X)
Solve X= 5 15 (approximately equal to)
You need to buy another 5 15 shares, but the purchase can only be an integer multiple of 100, so you have to buy 600 shares in practice.