Unformatted text preview: i.e. between µ3σ and µ+3σ). More precisely [but you just need to remember the rounded values 68 , 95 & 99.7] Eg. Standard normal Curve Example: SAT SCORE
v༇ Verbal SAT scores for collegebound seniors in 1999
have approximately normal distribution with µ = 505
and σ = 110. q༇ What is the proportion of scores below 615? Example (cont.)
Start by drawing a picture Example (cont.)
Note: 615 is 1 SD above the mean. (615 = 505 + 110) Want
this area: Example (cont.)
68 % 16 % 16 %
395 505 615 Answer = 16% + 68% = 84% Useful property of normal distributions:
The Z Score
If variable X is normally distributed with mean µ
and standard deviation σ, then the variable Z Z= X −µ σ is normally distributed with mean 0 and standard
deviation 1 (standard normal). ZScore & Key consequen...
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 Fall '07
 Lv
 Normal Distribution, standard normal curve

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