SOLUTION: 4. scores on an achievement test are known to be normally distributed with a mean of 420 and a standard deviation of 80. a. what is the probability of a score between 400 and 480?

Question 1197884: 4. scores on an achievement test are known to be normally distributed with a mean of 420 and a standard deviation of 80. a. what is the probability of a score between 400 and 480? b. what is the minimum test score needed in order to be in the top 5 % of all people taking the test?
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
Normal Distribution: µ = 420 and σ = 80
Using a hand held TI or similarly an inexpensive calculator like an Casio fx-115 ES plus
a. P( 400 ≤ x ≤ 480) = normcdf(400,480,420,80) = .3721
b. Invnorm(.95) = 1.645
x = 1.645*80 + 420 = 551.6
552 the minimum test score needed in order to be in the top 5 % of all people taking the test
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