The "test variable" functionality plays an essential role in the split test process.

“测试变量”功能在分割测试过程中扮演着重要的角色。

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This section of the course develops the mathematical concepts used in statistics. Three ideas are essential: Random Variable, Density Functions, and Expectations.

此部分课程扩展了统计学中的基本数学概念。三个基本想法如下：随机变数，密度函数与期望。

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The math model is used to image the essential relation of every variable in the process, maybe the model is algebra equation, or differential equation, or geometry curve.

数学模型用来反映过程本身各有关变量之间本质关系，它可能是代数方程、微分方程或几何曲线。

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Pre-payment allows customers with variable and unpredictable incomes to pay what they can, when they can, for an essential service.

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