If one amount is proportional to another, the two amounts increase and decrease at the same rate so there is always the same relationship between them.
双语例句
例： Loss of weight is directly proportional to the rate at which the disease is progressing.
体重下降和该病的发展速度成正比。
例： a proportional fee based on the final sale price.
一种以最后销售价为基础计算的比例费用。