If the purchase price at the beginning of the month is a yuan and the profit rate at the beginning of the month is x, the sales price at the beginning of the month is a( 1+x) yuan, the purchase price at the end of the month is a( 1-8%) yuan, and the sales price is a (1+x). Get a (1+x) = a (1-8%) [1+(x+10%)] because A > 0, if both sides are divided by a at the same time,1+x = (/.

1. Profit rate is the ratio of surplus value to all prepaid capital, and profit rate is the conversion form of surplus value rate, which is another ratio calculated by different methods for the same surplus value. If P' stands for profit rate and c stands for all prepaid capital (c+v), then profit rate P'= M/C = M/(C+V).

Second, the profit rate is a relative index reflecting the profit level of an enterprise in a certain period of time. Profit rate index can not only assess the completion of enterprise profit plan, but also compare the management level between enterprises and in different periods to improve economic benefits. Cost profit rate = profit/cost × 100%, and sales profit rate = profit/sales × 100%.

Three: the main factors

Profit rate refers to the conversion of surplus value into profit and the conversion of surplus value rate into profit rate. Profit margin is the ratio of surplus value to all prepaid capital. Profit rate and surplus value rate are different ratios obtained by comparing the same surplus value with different amounts of capital. The profit rate indicates the appreciation degree of all prepaid capital, which is always less than the surplus value rate in quantity, thus covering up the exploitation degree of capitalism.

Four: problem analysis

Under the capitalist system, the profit rate tends to decrease. This is because, with the development of capitalist industries, the organic composition of capital is constantly improving, which will inevitably lead to a decline in profit margins. But this is only one aspect of the problem. In addition, we should also see that a series of factors are hindering and delaying the decline of profit margin. For example, with the development of capitalism, the exploitation of workers by capitalists is constantly strengthening; Due to the improvement of labor productivity, the value of production materials such as machinery, equipment and raw materials is also declining.

In addition, capitalist countries can also improve their profit margins through unequal exchange of foreign trade. Therefore, Marx said: "Generally speaking, we have seen that the same reason that causes the decline of general profit rate will have the opposite effect, hinder its decline, ease its decline, and partially weaken it. Therefore, this law only works as a tendency; Its role will only be clearly displayed under certain circumstances and after a long period of time. "