Albeno69 (stupid) further questions!

[Albeno69]

hey i have a sac coming up soon not sure when, stupid teacher went to Italy.
how do i do a 3 median line method.
i comprehend that if you have,
11 points are divided into 4/3/4.
10 points are divide into 3/4/3.
12 points are divided into 4/4/4.
but after this step i am completely lost.
could someone explain how to do this?

[Gloamglozer]

I know the book is a little ambiguous about the explanation so I'll try my best into giving you my own explanation.  So please yell out if you still have any further enquiries.

1.  You've done the first step correctly.  Basically the rule is that if you can't divide it evenly and there is one extra point, put it in the middle region.  if there are two spare points, put one in each of the outer regions.
2.  Now that you have divided up the points into groups, we are going to find the median point in each group.  You need to do this in two steps:

• Firstly, find the median of the x values. 
• Just say for the first group, we have 3 points of the coordinates (1,1), (2,2) & (3,1.5). 
• Put all the x coordinates in order.  So 1,2,3.
• The median is 2.

• Secondly, we find the median of the y values.
• Put all the y coordinates in order.  So 1, 1.5, 2.
• The median is 1.5.

3.  Now, we know the median point in the first region is (2, 1.5).
4.  Mark this point on the graph with a cross (or whatever tickles your fancy).
5.  Repeat steps 2-4 for the remaining groups.
6.  Place your ruler so that the ruler passes through the first and last median points.
7.  Now slide the ruler one third towards the middle cross/marker.
8.  Rule the line.
9.  There you have it, your three median line.

Another and faster way if doing it would be to do step 2 visually but in a SAC, I'm pretty sure they'll ask you to calculate the gradient and possibly y-intercept of the line and if you do it visually, then you might end up with a gradient that could be very inaccurate from the "range" that your teachers would accept as the correct answer.

[Albeno69]

I know the book is a little ambiguous about the explanation so I'll try my best into giving you my own explanation.  So please yell out if you still have any further enquiries.

1.  You've done the first step correctly.  Basically the rule is that if you can't divide it evenly and there is one extra point, put it in the middle region.  if there are two spare points, put one in each of the outer regions.
2.  Now that you have divided up the points into groups, we are going to find the median point in each group.  You need to do this in two steps:

• Firstly, find the median of the x values. 
• Just say for the first group, we have 3 points of the coordinates (1,1), (2,2) & (3,1.5). 
• Put all the x coordinates in order.  So 1,2,3.
• The median is 2.

• Secondly, we find the median of the y values.
• Put all the y coordinates in order.  So 1, 1.5, 2.
• The median is 1.5.

3.  Now, we know the median point in the first region is (2, 1.5).
4.  Mark this point on the graph with a cross (or whatever tickles your fancy).
5.  Repeat steps 2-4 for the remaining groups.
6.  Place your ruler so that the ruler passes through the first and last median points.
7.  Now slide the ruler one third towards the middle cross/marker.
8.  Rule the line.
9.  There you have it, your three median line.

Another and faster way if doing it would be to do step 2 visually but in a SAC, I'm pretty sure they'll ask you to calculate the gradient and possibly y-intercept of the line and if you do it visually, then you might end up with a gradient that could be very inaccurate from the "range" that your teachers would accept as the correct answer.

thanks i have a dud of a teacher who compares maths to religion.lol
just wondering say you are given 4 points what would you do?

[Gloamglozer]

thanks i have a dud of a teacher who compares maths to religion.lol
just wondering say you are given 4 points what would you do?

Your welcome.  Are you saying 4 points to plot a three median line for?  If that is the case, I'm pretty sure you can't do one because you wouldn't be able to divide the points, let alone be able to draw a median line accurately since you'll end up with one point in the first and last group.  But unfortunately, I'm not too pro enough you answer that question so perhaps someone with more knowledge might be more certain.

[Albeno69]

thanks i have a dud of a teacher who compares maths to religion.lol
just wondering say you are given 4 points what would you do?

Your welcome.  Are you saying 4 points to plot a three median line for?  If that is the case, I'm pretty sure you can't do one because you wouldn't be able to divide the points, let alone be able to draw a median line accurately since you'll end up with one point in the first and last group.  But unfortunately, I'm not too pro enough you answer that question so perhaps someone with more knowledge might be more certain.

na like 4/3/4. sorry for the confusion.

[Gloamglozer]

thanks i have a dud of a teacher who compares maths to religion.lol
just wondering say you are given 4 points what would you do?

Your welcome.  Are you saying 4 points to plot a three median line for?  If that is the case, I'm pretty sure you can't do one because you wouldn't be able to divide the points, let alone be able to draw a median line accurately since you'll end up with one point in the first and last group.  But unfortunately, I'm not too pro enough you answer that question so perhaps someone with more knowledge might be more certain.

na like 4/3/4. sorry for the confusion.

Not a problem.  You would do the same thing.  If you have four points in the first and last group, then you would follow step 2 of my explanation.  Just say you had these four points:

(1,3), (3,5), (2,6) & (5,4).

1.  Put all the x-coordinates in order - 1,2,3,5.
2.  Take the median.  In this case, it would fall between 2 & 3.
3.  To find the median, you would do .  That equals to 2.5.
4.  Put all the y-coordinates in order - 3,4,5,6.
5.  Take the median.  In this case, it would fall between 4 & 5.
6.  To find the median, you would do .  That equals to 4.5.
7.  Therefore, the median point for that group would be (2.5,4.5).

[Albeno69]

thanks i have a dud of a teacher who compares maths to religion.lol
just wondering say you are given 4 points what would you do?

Your welcome.  Are you saying 4 points to plot a three median line for?  If that is the case, I'm pretty sure you can't do one because you wouldn't be able to divide the points, let alone be able to draw a median line accurately since you'll end up with one point in the first and last group.  But unfortunately, I'm not too pro enough you answer that question so perhaps someone with more knowledge might be more certain.

na like 4/3/4. sorry for the confusion.

Not a problem.  You would do the same thing.  If you have four points in the first and last group, then you would follow step 2 of my explanation.  Just say you had these four points:

(1,3), (3,5), (2,6) & (5,4).

1.  Put all the x-coordinates in order - 1,2,3,5.
2.  Take the median.  In this case, it would fall between 2 & 3.
3.  To find the median, you would do .  That equals to 2.5.
4.  Put all the y-coordinates in order - 3,4,5,6.
5.  Take the median.  In this case, it would fall between 4 & 5.
6.  To find the median, you would do .  That equals to 4.5.
7.  Therefore, the median point for that group would be (2.5,4.5).

you are the best thanks you

[Gloamglozer]

You're welcome.    Best of luck on the upcoming SAC and wish you all the best in 2010. 

[Albeno69]

another question just to clarify is x always the independent and y always the dependent variable. and do u have any hint on how to distinguish between the two im really struggling on witch is witch and how to tell them apart.
thanks.

[stonecold]

generally yes, the x is the independent variable, and the y is the dependent.  there are exceptions though.

a rule which you can follow is the independent variable is always plotted on the horizontal axis (known as the x-axis), whilst the dependent variable is on the vertical axis. (known as the y-axis)

on last years exam 1, they gave us a two columns of data.  normally you would plot the left column as x variable, and the right column as y variable. the question said to use the right column as the independent variable, so you had to switch the columns in your calc to get the right equation.

to make it more complicated the the columns were named age and sleep time or something like that.
normally you would use age (left column) as independent, and sleep time(right column) as dependent
however this question said to use sleep time as the independent variable, so in your calc, you have to put the sleep time list on the left and the age list on the right, basically the opposite to how it appeared on the paper....

then just do your normal stat calc function and get the equation of the line, r value or whatever it's asking for...

[nex]

I've found a great way to distinguish between the dependant and independant variable is to construct a sentence from it, and see which option makes more logical sense. For example, Height and Time. The two sentences would be either 1) Height is dependant on time or 2) Time is dependant on height. The 2nd sentence doesn't make sense at all, while the first one is completely logical, so therefore, height is the dependant variable, and time is the independant variable.

[Albeno69]

thanks

[Visionz]

I've found a great way to distinguish between the dependant and independant variable is to construct a sentence from it, and see which option makes more logical sense. For example, Height and Time. The two sentences would be either 1) Height is dependant on time or 2) Time is dependant on height. The 2nd sentence doesn't make sense at all, while the first one is completely logical, so therefore, height is the dependant variable, and time is the independant variable.

This is how I did it. My sentence is simply "______ depends on _________" Height depends on weight - no. weight depends on height - yes. Whichever makes more sense.

I used to label independent variables, dependent, 100% of the time. I found that my issue was completely retarded. I thought in my head that dependent meant independent. I think it was because the in- prefix has a negative connotation.. sort of.. like inconsiderate and incomprehensible. Comprehensible is the same as independent but dependent is the same as incomprehensible. It was adjective is 'weaker' or something. I dunno. I dont expect anyone to understand, especially when I dont.

[Martoman]

I've found a great way to distinguish between the dependant and independant variable is to construct a sentence from it, and see which option makes more logical sense. For example, Height and Time. The two sentences would be either 1) Height is dependant on time or 2) Time is dependant on height. The 2nd sentence doesn't make sense at all, while the first one is completely logical, so therefore, height is the dependant variable, and time is the independant variable.

This is how I did it. My sentence is simply "______ depends on _________" Height depends on weight - no. weight depends on height - yes. Whichever makes more sense.

I used to label independent variables, dependent, 100% of the time. I found that my issue was completely retarded. I thought in my head that dependent meant independent. I think it was because the in- prefix has a negative connotation.. sort of.. like inconsiderate and incomprehensible. Comprehensible is the same as independent but dependent is the same as incomprehensible. It was adjective is 'weaker' or something. I dunno. I dont expect anyone to understand, especially when I dont.

This is the EXACT method I use.

[Albeno69]

I've found a great way to distinguish between the dependant and independant variable is to construct a sentence from it, and see which option makes more logical sense. For example, Height and Time. The two sentences would be either 1) Height is dependant on time or 2) Time is dependant on height. The 2nd sentence doesn't make sense at all, while the first one is completely logical, so therefore, height is the dependant variable, and time is the independant variable.

This is how I did it. My sentence is simply "______ depends on _________" Height depends on weight - no. weight depends on height - yes. Whichever makes more sense.

I used to label independent variables, dependent, 100% of the time. I found that my issue was completely retarded. I thought in my head that dependent meant independent. I think it was because the in- prefix has a negative connotation.. sort of.. like inconsiderate and incomprehensible. Comprehensible is the same as independent but dependent is the same as incomprehensible. It was adjective is 'weaker' or something. I dunno. I dont expect anyone to understand, especially when I dont.

This is the EXACT method I use.

yea now that what im using to and i actually understand what im doing now. it is so much easier when u understand something.lol