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The standard deviation measures how much each reading differs from the mean (mathematic average) of all of the readings.
A frequency distribution is a table of values of one or more variables that make a sample. Each entry in the table contains the frequency (or count) of the occurrences of values within a particular group, and this way the table summarizes the distribution of values in the sample.
from Red Crab Manual:
A list starts with a bracket ( [ ) and ends with a bracket ( ] ) and has commas between the elements of the list.
n=sum(y) is the number of the elements in the list.
SVari(x) is the variance of sample values in a list
SStDev(x) is the sample standard deviation of values in a list.
Mean(x) is the mathematical average value of a list.
each group is considered to be a sample from a distinct population
the responses in each group are independent of those in the other group
the distributions of the variable of interest are normal
A 't' test compares the means of two groups.
The null hypothesis is that the two population means are equal to each other. To test the null hypothesis, you need to calculate the following values: (x1, x2)(the means of the two samples), s1², s2² (the variances of the two samples), n1, n2 (the sample sizes of the two samples), and k (the degrees of freedom).
Contents: Addition; Subtraction; The use of Double Signs and Brackets; Multiplication; Division; Simple Equations; The Lowest Common Multiple; Fractions; Quadratic Equations; Simultaneous Equations; Exponential Notation.
For a generation this was the leading textbook on the subject of plane geometry in America. Topics covered: rectilinear figures, the circle, proportion, similar polygons, areas of polygons, regular polygons and circles, etc.