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  • hba

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  • hba
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  • hba
Actually i know. \[Mean=\sum_{}^{}fx/\sum_{}^{}f\] I know, \[\sum_{}^{}f=2000\]
do you have the answer key is the answer 7.975 ???

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Other answers:

  • hba
I also think that is the answer as i tried doing it.
  • hba
But here x1,x2,x3 cannot be 8.5,7.5 and 8 because it is actually the mean
  • hba
As mentioned in the ques
Okay give me a second.
  • hba
Now suppose that we call \[ \sum fx \]The 'total'
We want the 'total' of each sub population.
Then we can add them
To get the 'total' of the whole population.
From there we can find the mean of the whole population.
We know that the sum is \(700 \times 8.5 + 800 \times 7.5 + 500 \times 8\)
  • hba
No No No 8.5,7.5 and 8 cannot be x
  • hba
They are the means
Yeah, but he's not using that formula.
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.
He using this: \[ \sum fx = \frac{\sum fx}{\sum f}\times \sum f \]
Can you continue from this point?
i don't think there is any problem with taking them as x's . what you alreadyy did is correct 7.975 .
lunch... g2g
  • hba
But how can you say mean of x is actually x?
(8.5*700 + 800*7.5 + 500*8)/2000
these are different random variables for the whole population . you can just use them in the formula .
  • hba
@wio Please justify
  • hba
It says that it is the mean @sami-21
Okay so if you have three means... suppose they are \(m_1, m_2, m_3\)
\[ m_1 = \frac{\sum_1fx}{\sum_1f} \]
yes it does says . and requires the mean for population . which should be taking the means of the sub populatiions .
  • hba
One more thing,If that is not the formula,What is it?
  • hba
@xoya Shu away
the mean of all three will be: \[ m_4 = \frac{\sum_4 fx}{\sum_4x} = \frac{\sum_1 fx + \sum_2 fx+ \sum_3 fx}{\sum_1 f + \sum_2 f + \sum_3 f} \]
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.
Notice how \[ m_1 = \frac{\sum_1 fx}{\sum_1 f} \implies m_1\sum_1 f = \sum_1 f x \]
  • hba
Okay so what would the formula basically?
  • hba
Given means... \(m_1, m_2, \dots \) with total frequencies \(f_1,f_2,...\) then the mean of the totals is: \[ \frac{\sum m_if_i}{\sum f_i} \]
  • hba
Thanks a lot :D :D
It's not the same formula, they just happen to be the same though by coincidence.
  • hba
I see.

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