Standard Deviation

Question

The mean Algebra 2 test score is 81.5, with a standard deviation of 5.1. There are 130 students taking the course. Assuming a normally distributed curve, how many students scored below 76.4? Remember: You can't have a fraction of a person. Round if necessary.  (Remember to use the percents given by the book: 2.35%, 13.5%, 34%.)

Answer 1

Hi Tin. There were 21 students who scored below 76.4.

This is because 76.4 is 1 standard deviation below the mean. (81.5-5.1=76.4)

That means that 15.9% scored below 76.4. (50, which is the mean percent, minus 19.1, minus 15.0, gives you 15.9).

15.9%= .159, and .159 x 130 students = 20.67, which we round to 21.

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