## hba Group Title Stats help required one year ago one year ago

1. hba Group Title

2. hba Group Title

Actually i know. $Mean=\sum_{}^{}fx/\sum_{}^{}f$ I know, $\sum_{}^{}f=2000$

3. sami-21 Group Title

4. hba Group Title

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

5. hba Group Title

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

6. hba Group Title

As mentioned in the ques

7. wio Group Title

Okay give me a second.

8. hba Group Title

Sure

9. wio Group Title

Now suppose that we call $\sum fx$The 'total'

10. wio Group Title

We want the 'total' of each sub population.

11. wio Group Title

12. wio Group Title

To get the 'total' of the whole population.

13. wio Group Title

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

14. ParthKohli Group Title

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

15. hba Group Title

No No No 8.5,7.5 and 8 cannot be x

16. hba Group Title

They are the means

17. wio Group Title

Yeah, but he's not using that formula.

18. ParthKohli Group Title

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.

19. wio Group Title

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

20. ParthKohli Group Title

Can you continue from this point?

21. sami-21 Group Title

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

22. ParthKohli Group Title

lunch... g2g

23. hba Group Title

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

24. sami-21 Group Title

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

25. sami-21 Group Title

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

26. hba Group Title

27. hba Group Title

It says that it is the mean @sami-21

28. wio Group Title

Okay so if you have three means... suppose they are $$m_1, m_2, m_3$$

29. wio Group Title

$m_1 = \frac{\sum_1fx}{\sum_1f}$

30. sami-21 Group Title

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

31. hba Group Title

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

32. hba Group Title

@xoya Shu away

33. wio Group Title

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

34. wio Group Title

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.

35. wio Group Title

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

36. hba Group Title

Okay so what would the formula basically?

37. hba Group Title

be*

38. wio Group Title

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

39. hba Group Title

Thanks a lot :D :D

40. wio Group Title

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

41. hba Group Title

I see.