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Maths statistics

The marks of 24 students in a test had mean m and standard deviation 6. Two new students took the same test. Their marks were m-4 and m+4.
Show that the standard deviation of the marks of all 26 students is 2.60, correct to 3 significant figures.
Reply 1
Avatar for mqb2766
mqb2766
21
What are you stuck with / what have you tried?
Note your question is wrong. The standard deviation going from 6 to 2.6 is impossible with just two new marks.
(edited 2 years ago)
Reply 2
Avatar for United156
United156
OP
2
I laid out the standard deviation equation and tried to find a value for m, but I couldn’t unfortunately. :frown:
Reply 3
Avatar for davros
davros
16
Original post by United156
I laid out the standard deviation equation and tried to find a value for m, but I couldn’t unfortunately. :frown:

Can you upload an image of the original question? mqb is suggesting that the question doesn't work as you've posted it!
Reply 4
Avatar for mqb2766
mqb2766
21
Original post by davros
Can you upload an image of the original question? mqb is suggesting that the question doesn't work as you've posted it!

I believe the std dev is sqrt(6).
Original post by United156
I laid out the standard deviation equation and tried to find a value for m, but I couldn’t unfortunately. :frown:

You need to use the formula for the variance. You know what the new mean is, so you can compute what effect the two additional points has on the variance.
(edited 2 years ago)
Reply 5
Avatar for United156
United156
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2
Original post by davros
Can you upload an image of the original question? mqb is suggesting that the question doesn't work as you've posted it!

image.jpg
Reply 6
Avatar for United156
United156
OP
2
Original post by mqb2766
I believe the std dev is sqrt(6).

You need to use the formula for the variance. You know what the new mean is, so you can compute what effect the two additional points has on the variance.

Unfortunately that’s where I’m stuck.
Reply 7
Avatar for mqb2766
mqb2766
21
Original post by United156
Unfortunately that’s where I’m stuck.

What are you stuck with?
The two formulae for variance are given in formula sheet / textbook / ...
Reply 8
Avatar for United156
United156
OP
2
Original post by mqb2766
What are you stuck with?
The two formulae for variance are given in formula sheet / textbook / ...

The whole question
Reply 9
Avatar for mqb2766
mqb2766
21
Original post by United156
The whole question

Given that there are only a couple of formulae for varaince, which have you tried using, why are you stuck ...

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