Don't use the concept of profit rate, try to calculate net profit directly with integral. For example, if you play three hands and earn 10 points per hand, then your profit per hand is 10 points * 10 yuan/point = 100 yuan. The third hand, 300 yuan. Here, don't care how much money you invest, what is the specific rate of return. This thing is meaningless and makes you dizzy easily. Just count directly.