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# S1 - Standard deviation Watch

1. This is my method

SQRT [ 1^2 + 2^2 + 3^2 - (1+2+3)^2 ]

I get the wrong answer I dont know why ?
2. (Original post by IShouldBeRevising_)

This is my method

SQRT [ 1^2 + 2^2 + 3^2 - (1+2+3)^2 ]

I get the wrong answer I dont know why ?
Don't you think the probabilities might be useful?
3. (Original post by BabyMaths)
Don't you think the probabilities might be useful?
Oh yeah I was just going of the s.d formula the exam solution guy used in his vid...

s.d = sqrt ( sum x^2 - x bar squared )
4. (Original post by IShouldBeRevising_)
Oh yeah I was just going of the s.d formula the exam solution guy used in his vid...

s.d = sqrt ( sum x^2 - x bar squared )
You need

and

5. (Original post by BabyMaths)
You need

and

Oh yes its just clicked...

S.d = sqrt of var (X)

Nice one

Was looking at the wrong section on exam solutions so got confused lol
6. Find the variance and square root it.
7. (Original post by BabyMaths)
You need

and

The first part I thought the srcc would be positive as there is a relation ship between the variables as the distance travelled increases the satifsafction decreasses however the answer is -1?
8. The ranks are

1 2 3 4 5 6 7
7 6 5 4 3 2 1

This gives a result of .

If the ranks were

1 2 3 4 5 6 7
1 2 3 4 5 6 7

then this would give .
9. (Original post by BabyMaths)
The ranks are

1 2 3 4 5 6 7
7 6 5 4 3 2 1

This gives a result of .

If the ranks were

1 2 3 4 5 6 7
1 2 3 4 5 6 7

then this would give .
ohhh... I see thank you

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