变量按性质可分为三种情况。第一种,两个变量均为非随机变量,如欧姆定律:I=V/P,变量之间有某种确定的关系;第二种,一个变量是非随机变量,另一个变量是随机变量,如水灰比与混凝土抗压强度的关系;第三种,二个变量均为随机变量,如混凝土快速强度与标准强度之间的关系。严 Variables can be divided into three situations by nature. First, both variables are non-random variables, such as Ohm’s law: I=V/P, there is a certain relationship between variables; second, one variable is a non-random variable, and the other is a random variable. For example, the relationship between water-cement ratio and the compressive strength of concrete; the third and the two variables are random variables, such as the relationship between the rapid strength of concrete and the standard strength. strict