Question

Stats help required

Answer 1

Actually i know.

\[Mean=\sum_{}^{}fx/\sum_{}^{}f\]

I know,

\[\sum_{}^{}f=2000\]

Answer 2

do you have the answer key
is the answer 7.975 ???

Answer 3

I also think that is the answer as i tried doing it.

Answer 4

But here x1,x2,x3 cannot be 8.5,7.5 and 8 because it is actually the mean

Answer 5

As mentioned in the ques

Answer 6

Okay give me a second.

Answer 7

Sure

Answer 8

Now suppose that we call \[
\sum fx
\]The 'total'

Answer 9

We want the 'total' of each sub population.

Answer 10

Then we can add them

Answer 11

To get the 'total' of the whole population.

Answer 12

From there we can find the mean of the whole population.

Answer 13

We know that the sum is \(700 \times 8.5 + 800 \times 7.5 + 500 \times 8\)

Answer 14

No No No 8.5,7.5 and 8 cannot be x

Answer 15

They are the means

Answer 16

Yeah, but he's not using that formula.

Answer 17

Since mean is sum of observations divided by number of observations, we know that the sum of observations multiplied by the number of observations is the sum of observations.

Answer 18

He using this: \[
\sum fx = \frac{\sum fx}{\sum f}\times \sum f
\]

Answer 19

Can you continue from this point?

Answer 20

i don't think there is any problem with taking them as x's .
what you alreadyy did is correct
7.975 .

Answer 21

lunch... g2g

Answer 22

But how can you say mean of x is actually x?

Answer 23

(8.5*700 + 800*7.5 + 500*8)/2000

Answer 24

these are different random variables for the whole population . you can just use them in the formula .

Answer 25

@wio Please justify

Answer 26

It says that it is the mean @sami-21

Answer 27

Okay so if you have three means... suppose they are \(m_1, m_2, m_3\)

Answer 28

\[
m_1 = \frac{\sum_1fx}{\sum_1f}
\]

Answer 29

yes it does says . and requires the mean for population . which should be taking the means of the sub populatiions .

Answer 30

One more thing,If that is not the formula,What is it?

Answer 31

@xoya Shu away

Answer 32

the mean of all three will be: \[
m_4 = \frac{\sum_4 fx}{\sum_4x} = \frac{\sum_1 fx + \sum_2 fx+ \sum_3 fx}{\sum_1 f + \sum_2 f + \sum_3 f}
\]

Answer 33

This is because the total frequency \(\sum_4 f\) is the sum of the sub frequencies. The total weight \(\sum_4 fx\) is equal to the sum of all the weights.

Answer 34

Notice how \[
m_1 = \frac{\sum_1 fx}{\sum_1 f} \implies m_1\sum_1 f = \sum_1 f x
\]

Answer 35

Okay so what would the formula basically?

Answer 36

be*

Answer 37

Given means... \(m_1, m_2, \dots \) with total frequencies \(f_1,f_2,...\) then the mean of the totals is: \[
\frac{\sum m_if_i}{\sum f_i}
\]

Answer 38

Thanks a lot :D :D

Answer 39

It's not the same formula, they just happen to be the same though by coincidence.

Answer 40

I see.