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hba Group Title

Stats help required

  • one year ago
  • one year ago

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  1. hba Group Title
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    • one year ago
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  2. hba Group Title
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    Actually i know. \[Mean=\sum_{}^{}fx/\sum_{}^{}f\] I know, \[\sum_{}^{}f=2000\]

    • one year ago
  3. sami-21 Group Title
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    do you have the answer key is the answer 7.975 ???

    • one year ago
  4. hba Group Title
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    I also think that is the answer as i tried doing it.

    • one year ago
  5. hba Group Title
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    But here x1,x2,x3 cannot be 8.5,7.5 and 8 because it is actually the mean

    • one year ago
  6. hba Group Title
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    As mentioned in the ques

    • one year ago
  7. wio Group Title
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    Okay give me a second.

    • one year ago
  8. hba Group Title
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    Sure

    • one year ago
  9. wio Group Title
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    Now suppose that we call \[ \sum fx \]The 'total'

    • one year ago
  10. wio Group Title
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    We want the 'total' of each sub population.

    • one year ago
  11. wio Group Title
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    Then we can add them

    • one year ago
  12. wio Group Title
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    To get the 'total' of the whole population.

    • one year ago
  13. wio Group Title
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    From there we can find the mean of the whole population.

    • one year ago
  14. ParthKohli Group Title
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    We know that the sum is \(700 \times 8.5 + 800 \times 7.5 + 500 \times 8\)

    • one year ago
  15. hba Group Title
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    No No No 8.5,7.5 and 8 cannot be x

    • one year ago
  16. hba Group Title
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    They are the means

    • one year ago
  17. wio Group Title
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    Yeah, but he's not using that formula.

    • one year ago
  18. ParthKohli Group Title
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    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.

    • one year ago
  19. wio Group Title
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    He using this: \[ \sum fx = \frac{\sum fx}{\sum f}\times \sum f \]

    • one year ago
  20. ParthKohli Group Title
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    Can you continue from this point?

    • one year ago
  21. sami-21 Group Title
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    i don't think there is any problem with taking them as x's . what you alreadyy did is correct 7.975 .

    • one year ago
  22. ParthKohli Group Title
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    lunch... g2g

    • one year ago
  23. hba Group Title
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    But how can you say mean of x is actually x?

    • one year ago
  24. sami-21 Group Title
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    (8.5*700 + 800*7.5 + 500*8)/2000

    • one year ago
  25. sami-21 Group Title
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    these are different random variables for the whole population . you can just use them in the formula .

    • one year ago
  26. hba Group Title
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    @wio Please justify

    • one year ago
  27. hba Group Title
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    It says that it is the mean @sami-21

    • one year ago
  28. wio Group Title
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    Okay so if you have three means... suppose they are \(m_1, m_2, m_3\)

    • one year ago
  29. wio Group Title
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    \[ m_1 = \frac{\sum_1fx}{\sum_1f} \]

    • one year ago
  30. sami-21 Group Title
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    yes it does says . and requires the mean for population . which should be taking the means of the sub populatiions .

    • one year ago
  31. hba Group Title
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    One more thing,If that is not the formula,What is it?

    • one year ago
  32. hba Group Title
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    @xoya Shu away

    • one year ago
  33. wio Group Title
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    the mean of all three will be: \[ m_4 = \frac{\sum_4 fx}{\sum_4x} = \frac{\sum_1 fx + \sum_2 fx+ \sum_3 fx}{\sum_1 f + \sum_2 f + \sum_3 f} \]

    • one year ago
  34. wio Group Title
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    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.

    • one year ago
  35. wio Group Title
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    Notice how \[ m_1 = \frac{\sum_1 fx}{\sum_1 f} \implies m_1\sum_1 f = \sum_1 f x \]

    • one year ago
  36. hba Group Title
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    Okay so what would the formula basically?

    • one year ago
  37. hba Group Title
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    be*

    • one year ago
  38. wio Group Title
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    Given means... \(m_1, m_2, \dots \) with total frequencies \(f_1,f_2,...\) then the mean of the totals is: \[ \frac{\sum m_if_i}{\sum f_i} \]

    • one year ago
  39. hba Group Title
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    Thanks a lot :D :D

    • one year ago
  40. wio Group Title
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    It's not the same formula, they just happen to be the same though by coincidence.

    • one year ago
  41. hba Group Title
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    I see.

    • one year ago
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