Working out the mean (maths)

[Henry Hawthorne]

Got a fairly simple question I need to answer but for some reason I cannot work out how to do it at all...



Question 3 (b)... Any pointers?

Thanks.

[Iain328]

Henry Hawthorne said:

Got a fairly simple question I need to answer but for some reason I cannot work out how to do it at all...



Question 3 (b)... Any pointers?

Thanks.

Take the median value for each group & then do a weighted average of all the groups?

[pacey_sot]

Been a while since my GCSEs but i think you just use the middle of the grouping i.e. you would assume you had 2 lots of 2.5, and so on

[eightseventhree]

Mean = Average Value, Calculated by adding all the observations and dividing by the number of observations.

[nail_it]

Easy peasy
Once you've got your median, your on your way.
And the final questions you can coast

[nail_it]

eightseventhree said:

Mean = Average Value, Calculated by adding all the observations and dividing by the number of observations.

Correct

[Catz]

Don't you just add up all the frequencies then divide by the number of times available?

In other words 75 divide by 8 = 9.375 mins.

[Henry Hawthorne]

Catz said:

Don't you just add up all the frequencies then divide by the number of times available?

In other words 75 divide by 8 = 9.375 mins.

That's what I originally did... Is that the answer?

[dpbird90]

pacey_sot said:

Been a while since my GCSEs but i think you just use the middle of the grouping i.e. you would assume you had 2 lots of 2.5, and so on

Yep thas exactly how you do it, multiply the frequency by the midpoint of your range (e.g. 0-5 midpoint 2.5) for each frequency/range. Add up all the resulting values, divide by the number of groups.

[TVR MAN]

I think you take 2.5*2+7.5*9+12.5*23+....................+37.5*1

and then divide that by (2+9+23+...+1)

[samwilliams]

Henry Hawthorne said:

Catz said:

Don't you just add up all the frequencies then divide by the number of times available?

In other words 75 divide by 8 = 9.375 mins.

That's what I originally did... Is that the answer?

No, it isn't. As someone mentioned above, I think you'd substitute the time ranges for their middle value - i.e. 0-5 is taken as 2.5, 5-10 is taken as 7.5, etc. Then you work it out as though that is the value for each in that class.

So, you'd have 2 x 2.5 + 9 x 7.5 etc. divided by the sum of the frequencies. It'd probably come out around 15 or so. Certainly more than 9.

[nail_it]

75 is the grouped data!

[hairykrishna]

Henry Hawthorne said:

Catz said:

Don't you just add up all the frequencies then divide by the number of times available?

In other words 75 divide by 8 = 9.375 mins.

That's what I originally did... Is that the answer?

No. Look at the frequencies and apply some sense - does that look like a realistic value for the mean?

I think the mean is probably ~17 but I can't be arsed to calculate it.

[Henry Hawthorne]

samwilliams said:

Henry Hawthorne said:

Catz said:

Don't you just add up all the frequencies then divide by the number of times available?

In other words 75 divide by 8 = 9.375 mins.

That's what I originally did... Is that the answer?

No, it isn't. As someone mentioned above, I think you'd substitute the time ranges for their middle value - i.e. 0-5 is taken as 2.5, 5-10 is taken as 7.5, etc. Then you work it out as though that is the value for each in that class.

So, you'd have 2 x 2.5 + 9 x 7.5 etc. divided by the sum of the frequencies. It'd probably come out around 15 or so. Certainly more than 9.

Ah yes okay, I see! Perfect. Answer is 17.

Thanks guys. Don't ever remember doing this at GCSE!

[Henry Hawthorne]

inkiboo said:

How are you able to do the questions above if you are having trouble working out the mean of a set of values?

Don't know. The ones above are easy?

I know how to work out the mean usually (add up all the values then divide by the number of values) but I'd never done it from a table before so didn't know how to do it!

[ShadownINja]

Isn't this A-level standard?

[Henry Hawthorne]

International Baccalaureate.

[ShadownINja]

That's A-level equivalent, then?

[Henry Hawthorne]

Yes.

It's like a really st international equivalent of A-levels.