Two questions any help would be great
1. There is a normal distributed class average of 70 and a standard deviation of 10. So what would be the 20,60,80 percentiles???
2.There is a normal distributed class with average(mean) of 71 and a standard deviation of 11.Find the quartiles(Q1,Q2,Q3)?
Part 1a)
The 20th percentile in test scores is the test score which is surpassed by only 80% of the class. Likewise, the 60th percentile in test scores is the test score which is surpassed by only 40% of the class. Same deal with 80th percentile which is only surpassed by 20% of the class.
Now, let's call x the 20th percentile test score. How do we find x? Use the z-score equation: z =
We want the value of z that corresponds to .20. This value can be found using an online statistics applet (found in 30 seconds using google), or by reading your z-table (probably distributed countless number of times by your teacher and or in your text book). You will find that z = -0.84
So, plug and chug to get x: -0.84 =
Go from there and note that quartiles are the same question, just simply substitute for example, the first quartile with 25th percentile.