Question 734582: Please help. I'm not understanding this questions
The scores on a national test were normally distributed with a mean of 83 and a standard deviation of 8
To the nearest percent, what percentage of test takers scored between 70 and 90
15% of test takers scored below what test score? (Round to nearest test score)
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! The scores on a national test were normally distributed with a mean of 83 and a standard deviation of 8
To the nearest percent, what percentage of test takers scored between 70 and 90
z(70) = (70-83)/8 = -13/8
z(90) = (90-83)/8 = 7/8
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P(70< x <90) = P(-13/8 < z < 7/8) = normalcdf(-13/8,7/8) = 0.7571 = 75.71%
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15% of test takers scored below what test score? (Round to nearest test score)
Draw the picture:
Find the z-score with a left tail of 15%
invNorm(0.15) = -1.0364
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Find the corresponding score value:
x = z*s + u
x = -1.0364*8+83 = 74.71
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Cheers,
Stan H.
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