Students in a chemistry class convince their teacher to use the following "group grading" scenario. Students will all take the exam on their own; however, the grade they receive will be the mean of their test score with 4 other randomly selected classmates. Assume that the test scores for this particular exam are normally distributed with a mean of 74 and a standard deviation of 12 points. You need an 80 or better on this exam. What is the probability that your individual test score is above 80?
Solution :
Given that ,
mean = = 74
standard deviation = = 12
n = 4
= 74
= / n = 12/ 4 = 6
P( > 80) = 1 - P( < 80)
= 1 - P[( - ) / < (80-74) / 6]
= 1 - P(z < 1)
Using z table
= 1 - 0.8413
= 0.1587
probability= 0.1587
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