4-1. Random Variables
随机变量
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随机变量
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A random variable is a numerical quantity that is generated by a random experiment.
We will denote random variables by capital letters, such as or , and the actual values that they can take by lowercase letters, such as and .
Experiment
Roll two fair dice
Sum of the number of dots on the top faces
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
Flip a fair coin repeatedly
Number of tosses until the coin lands heads
1, 2, 3,4, …
Measure the voltage at an electrical outlet
Voltage measured
Operate a light bulb until it burns out
Time until the bulb burns out
A random variable is called discrete if it has either a finite or a countable number of possible values.
A random variable is called continuous if its possible values contain a whole interval of numbers.
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Number
Possible Values of