What happened last July 19, 2012?

    Last Thursday, our teacher has reviewed us about the topic confidence intervals for variances and standard deviation. She explained to us the use of the Chi- Square Distribution.

   Chi- Distribution is similar to the t distribution, it is like a family of curves based on the  number of degrees of freedom. it is obtain from the values of (n-1) S² / square of the standard deviation when a random sample are selected from a normally distributed.

   To get the confidence interval, you need to get the X² right which is obtain by subtracting the percentage of the confidence interval from 1 and then divide it by 2 and then find it to the row corresponding to the dgree of freedom and X²left which is obtain by subtracting the value of a/2 from 1 then find its row corresponding to its degree of freedom In finding the confidence interval for variances and standard deviation you will also need to  find the value of n,  and  standard deviation or variance. Then substitute it to formula.     

   Immediately after the discussion, our teacher  gave us a test  of two sets to avoid cheating. She also remind us about the rounding rule, the number of decimal places our answer should have and to read the given very well if it is a variance or standard deviation.

By: Dustin Joshua Esquia

      III- Gold