S1 and S2 DOUBTS HERE!!!!

[astarmathsandphysics]

1st questions above

[astarmathsandphysics]

last question above

[silvercameron]

I am taking CIE statistics 1 this year.
I have doubts relating to mean,median and mode. Although they are just the basics, i am still confused:

1) whenever we draw a histogram, do we always have to take 'frequency densities' on the y-axis? Or do we also take 'frequency' on the y-axis?

2) for grouped data, and the frequencies given, how do we find the median without drawing the cummulative frequency graph?

3) for grouped data, and frequencies given, how do we find the upper quartile and lower quartile?

4) what is the difference between variance and standard deviation?

Thanks.

[silvercameron]

anyone who can answer my questions? Pls.

[astarmathsandphysics]

You have to use frequency densities if the class intervals are not the same. Personally I think it is always better to use them cos you get used to them.
Variance = standard deviation squared.
For the median and quartile stuff see
http://www.astarmathsandphysics.com/a_level_maths_notes/S1/a_level_maths_notes_s1_quartiles_and_median_from_frequency_tables.html

[silvercameron]

^^thankyou.  now i can understand better and continue with my practice.

[astarmathsandphysics]

no probs

[silvercameron]

here's a question

Q) the mean snd standard deviation of the heights of 12 boys in a class are 148.8 and 5.4 cm respectively. A boy of height 153.4 cm joins the class. Find the mean and standard deviatiation of the 13 boys.

I found the mean but cant find SD.
____________________________

theres are formulas for finding median and quartiles in grouped data. But what if the data is not grouped and has large frequences and is summarised in a table.then how do we find the quartiles?

[astarmathsandphysics]

see attachment

[~ Miss Relina ~]

here is my question plz explain his answer

[astarmathsandphysics]

reasonable for the values given in the table as someone could easily practice 20 hours a week and professional musicians pactrice up to 60 or more. Not reasonable for 168 as only 168 hours in week.

[~ Miss Relina ~]

reasonable for the values given in the table as someone could easily practice 20 hours a week and professional musicians pactrice up to 60 or more. Not reasonable for 168 as only 168 hours in week.

Sir , I'm sorry but from where did you get these values ...is there anymore clarification

[astarmathsandphysics]

Number of hourse x between 1 and 15 and number of hours y between 4 and 18 in the table in your attachment

[~ Miss Relina ~]

reasonable for the values given in the table as someone could easily practice 20 hours a week and professional musicians pactrice up to 60 or more. Not reasonable for 168 as only 168 hours in week.

which  means that the graph will curve as it cease to be proportionalor form a linear relationship..........right  

[astarmathsandphysics]

Yes and it will definitetely curve as nutters practice 168 hours a week and make less than zero mistakes