Stats 151 - Z graph vs. T graph

Frage	Antworten
what is df?	Number of independent variables required to satisfy a certain condition. e.g. 3 + ? = 10
how are z and t curves different? how are they similar?	z does not depend on df = n-1 but t does. t has more spreading on its tails and a greater distribution. if he n is less then 30 they will have different shapes. they both have a bell curve. if n is greater then 30 then the shape are the same
if you are given the area if the tail of a t graph, how do you find the t alpha?	similar to what is done for a z graph where the mark given is Ta. df = degree of freedom
Measurments of acidity of rain water samples were recorded at 5 sites in a region, 3.5, 5.1, 5.0, 3.6, 4.8 (Ex = 22, Ex2= 99.26) give a 90% CI for the mean acidity of rain in that region	first find sd = square root(Ex2 – (Ex)2/n/n-1. should get 0.78. plug in the value of x bar and s into the equation of Xbar +/- ta/2 s/square root of n to get - 4.4 +/- ta/2 0.78/square root of 5- 4.4 +/- ta/2 0.78/square root of 5. 1-alpha is 0.90 minua this value from one and divide by 2 to get t under script 0.05. find the df which is n-1 = 4 use these two values to find the answer from table 4

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