The Normal Distribution and the 68-95-99.7 Rule

The Normal Distribution and the 68-95-99.7 Rule. In this video, I talk about the normal distribution and what percentage of observed values fall within either 1, 2, or 3 standard deviations from the mean. One specific example is discussed. For more free math video, visit

19 replies
  1. anabel0530
    anabel0530 says:

    would a score of say 120 be 1 or 2 standard deviations away? do you go by lines or by sections?

  2. Erika Harris
    Erika Harris says:

    Excellent explanation! Now if the question was: What percentage had an IQ between 115 and 55? How would you go about solving that?

  3. karan sharma
    karan sharma says:

    Thats fantastic buddy, thank you. Quick question – so lets say in your example Z scores is coming 1.8, which means 1.8 standard deviation above/below the mean. But how would we put this into confidence interval ? For instance, i know 1 SD means 68%, 2 SD means 95%….but how would we put 1.8 SD into a confidence interval ?

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