Interquartile range anyone?

Can anyone help me out?

I am doing some cwk and i'm a bit stuck.

we have to work out the interquartile range of a set of data :confused:

(something i've never covered before). I thought setting it out in a back-to-back stem and leaf diagram would be useful...So i've done that...

I think i have an idea but i just want to make sure i get it right

OK so i have 38 pieces of data (estimates)

does that mean the median = n (or 38) +1 ÷ 2 = 15 1/2 --- between the 15th and 16th scores

i need to work out the lower quartile and the upper quartile so i can get the interquartile... but im not quite sure how.

We were told the other week but i seem to have forgot and the text book isnt very clear.

I just want to know how to work out the interquartile of a set of data.... if anyone could help me out that would be fantastic.

Its probably quite straight forward...Excuse my ignorance :redface:

im not the best at maths. I did GCSE foundation in year 11 (and passed) but thought id give Intermediate a try... would really like a B :smile:

Many thanks,

Laus :smile:

Reply 1

*bobo*

8

LoopyLaus

Can anyone help me out?

I am doing some cwk and i'm a bit stuck.

we have to work out the interquartile range of a set of data :confused:

(something i've never covered before). I thought setting it out in a back-to-back stem and leaf diagram would be useful...So i've done that...

I think i have an idea but i just want to make sure i get it right

OK so i have 38 pieces of data (estimates)

does that mean the median = n (or 38) +1 ÷ 2 = 15 1/2 --- between the 15th and 16th scores

i need to work out the lower quartile and the upper quartile so i can get the interquartile... but im not quite sure how.

We were told the other week but i seem to have forgot and the text book isnt very clear.

I just want to know how to work out the interquartile of a set of data.... if anyone could help me out that would be fantastic.

Its probably quite straight forward...Excuse my ignorance :redface:

im not the best at maths. I did GCSE foundation in year 11 (and passed) but thought id give Intermediate a try... would really like a B :smile:

Many thanks,

Laus :smile:

Q₁ =38/4=9.5
when its a quartile you round the number up if it is to a decimal point to give you 10. Seems completely stupid and inaccurate rounding it up.
Q₃ = (38x3)/4=28.5
which you round up again to give you 28

Reply 2

LoopyLaus

OP

*bobo*

Q₁ =38/4=9.25
when its a quartile you round the number up if it is to a decimal point to give you 10. Seems completely stupid and inaccurate rounding it up.
Q₃ = (38x3)/4=27.75
which you round up again to give you 28

Thank you very much.

One problem :confused:

: my teacher said to do the number + 1 ÷ 2... that would give me 19 1/2.. which i would round up to 20?

I may have got it completely wrong.

So are you in year 10 - studying maths, doing your a-levels and then coming back to do your GCSE's?

Sorry for being difficult!

--------------

*Is impressed by your intelligence*

Reply 3

*bobo*

8

LoopyLaus

Thank you very much.

One problem :confused:

: my teacher said to do the number + 1 ÷ 2... that would give me 19 1/2.. which i would round up to 20?

I may have got it completely wrong.

So are you in year 10 - studying maths, doing your a-levels and then coming back to do your GCSE's?

Sorry for being difficult!

--------------

*Is impressed by your intelligence*

your doing the median above( Q₂ )- you don't round up the median
for the lower and upper quartiles, if:
for the lower you devide the number by 4, and recieve an integer, that is your number. However if you recieve a number to a decimal point then you round it up.
for the median- if you devide your number by 2 and recieve a decimal point you leave it as it is, but if it is an integer, you average it with the next consequtive integer (basically add 0.5)
I remeber this being slightly different at GCSE to Stats at A-level.

I'm taking my GCSEs at the same time as my maths a-level and open uni course.

Reply 4

LoopyLaus

OP

Thanks for the help :smile:

Reply 5

LoopyLaus

OP

*bobo*

Q₁ =38/4=9.5
when its a quartile you round the number up if it is to a decimal point to give you 10. Seems completely stupid and inaccurate rounding it up.
Q₃ = (38x3)/4=28.5
which you round up again to give you 28

Just one question - why do you times 38 by 3?

--------------

nm it makes perfect sense

Reply 6

LoopyLaus

OP

*bobo*

Q₁ =38/4=9.5
when its a quartile you round the number up if it is to a decimal point to give you 10. Seems completely stupid and inaccurate rounding it up.
Q₃ = (38x3)/4=28.5
which you round up again o give you 28

Hang on a sec - why do you round 9.5 to 10 but 28.5 to 28?