5lb chap 22,# 24

[anik1989]

A test is scored out of 100 and the scores are divided into five quintile groups. Students are not told their scores,
but only their quintile group.

Quanti ty A

The scores of two students in the bottom quintile
group, chosen at random and added together


Quanti ty B
The score of a student in the top
quintile group, chosen at random

explanation((Quintiles (“fifths” of the data) define relative scores, not absolute scores. Imagine two possible score
distributions:

Example 1: The class’s scores are 1, 2, 3, 4, 5 (20% of the class scored each of these). In this case, adding up two
lowest quintile students would be 1 + 1 = 2, which is less than 5, the score of a top quintile student.

Example 2: The class’s scores are 10, 11, 12, 13, 14 (20% of the class scored each of these — still not so sharp!). In
this case, adding up two lowest quintile students would be 10 + 10 = 20, which is greater than 14, the score of a top
quintile student.))

MY QUESTION IS WHAT DOES IT MEAN BY 1.FIVE QUINTILE?
2.IF 100 SCORE LIKE 1,2,3,8,9,30,45,67,87,56,34.. THEN HOW THEY ARE BECOME ONLY FIVE GROUPS??
3.WHY 20% of the class scored each of these ?? THEN WHAT ABOUT REST 80%???
4. IS THERE ANY ALTERNATIVE SIMPLE SOLUTION??

PLEASE EXPLAIN

[tommywallach]

Hey Anik,

Again, please aim for correct grammar in your posts, and no long strings of capital letters. : )

A quintile is a way of dividing a set of data into five groups (just as percentiles are a way to divide a set of data into a hundred groups). It has no effect on the actual data itself. For example, if the scores on a test are--1, 1, 4, 4, 7, 7, 10, 10, 13, 13--then the first quintile (20% of the data) is 1, the second is 4, and so on.

If the scores are 1, 1, 1, 1, 1, 1, 1, 1, 1, 1--then all the quintiles are one.

The reason why this question put 20% of the class in each quintile (instead of a bunch of random scores) is simply so that the math would be really easy. If you picked a million random scores, you're going to have to really look hard at the data. So you're welcome to do that, but it just makes life harder. Instead, we're just acting as if each quintile is ONE value (because it's POSSIBLE that each quintile was represented by only ONE test score), so we can add things up more easily.

-t

[anik1989]

ok, but two lowest student score should be, 1+2= 3, but they add first lowest score than again that number. i dont understand

[tommywallach]

Hey Anik,

No, because multiple students can get each score. So two students can both get a 1.

-t

[anik1989]

[quote="tommywallach"]Hey Anik,

No, because multiple students can get each score. So two students can both get a 1.

-thank you sir, but what if i say that the classes score { 1,1,1,1,1}
or {2,2,2,2,2}
here where is my fault??i dont understand this kind of math, would you please tell me where can i get a clear idea about this.

[tommywallach]

If the class scores 1, 1, 1, 1, 1, then the two lowest are 1 + 1 = 2.

If the class scores, 2, 2, 2, 2, 2, then the two lowest are 2 + 2 = 4.

-t