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Scores on a test have a mean of 66 and Q3 is 80. The scores have...

Scores on a test have a mean of 66 and Q3 is 80. The scores have a distribution that is approximately normal. Find the standard deviation. Round your answer to the nearest tenth. Group of answer choices 10.5 20.9 18.7 9.4

Math   Statistics-And-Probability   
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Homework Answers

Answer #1

Solution:-

Given that,

mean = = 66

x = 80

The z dist'n Third quartile is,

P(Z < z) = 75%

= P(Z < z) = 0.75  

= P(Z < 0.67 ) = 0.75

z = 0.67

Using z-score formula,

x = z * +

80 = 0.67 * + 66

= 80 - 66 / 0.67

= 20.9

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