Probabilities & Statistics 1 - OCR (not MEI) - jan 25th 2012 discussion

What was answer for spearman's rank question?

What was answer for spearman's rank question?

On the cumulative frequency graph question what did people put as the first 2 points? Technically the first one should have been 0,0 shouldn't it?

These are my answers. I haven't read the whole thread thoroughly, but I think they agree with what most people are saying:
1. i) 0.2
ii) 2.7
2. i) x is the independent variable as it is the variable that we are controlling
ii) -0.926 to 3 sf
iii) a) y=75.0-0.752x to 3 sf
b) At 25cm the estimate is reasonably reliable as we are interpolating within the depths which we have been studying and the pmcc is close to -1.
At 100cm the estimate is not reliable as we are extrapolating outside of the depths which we have been studying and we do not know if the relationship will continue beyond 48cm.
3. i) 0.526 to 3sf
ii) 0.399 to 3sf
4. a) 0.5
b) It will increase since the new entry will be ranked 6 by both. This will lead to d^2=0 and the numerator will remain unchanged, but the denominator will have increased.
5. i) a) 2
b) 0.667cm to 3sf
ii) (0.5,0), (3.5,6), (6.5,15) (I think these last two are the two they'll be looking for, but hopefully they'll be lenient as it's badly worded).
iii) a) 5.43, 3.08 to 3 sf
b) They are only estimates as they are based on a small sample size.6. i) V as each probability is less than the previous one (although this is impossible since P(X=0) should be 0)
ii) Y as it is a perfectly symmetrical which increases to a common mode, mean and median and then decreases
7. i) Geometric with p=0.6, assuming that the probability of an arrival of a woman is independent of previous arrivals, that this probability is constant for all arrivals and that we can classify each arrival as being either female or male.
ii) 0.0383
iii) 0.064
8. i) 0.0352 to 3sf
ii) a) 0.168 to 3sf
b) 0.416 to 3sf
9. i) a) 3024
b) 1680
ii) a) 5/14=0.357 to 3sf
b) 1/63 = 0.0159 to 3sf
Let me know if you disagree with any. I often make calculator errors on S1.

These are my answers. I haven't read the whole thread thoroughly, but I think they agree with what most people are saying:
1. i) 0.2
ii) 2.7
2. i) x is the independent variable as it is the variable that we are controlling
ii) -0.926 to 3 sf
iii) a) y=75.0-0.752x to 3 sf
b) At 25cm the estimate is reasonably reliable as we are interpolating within the depths which we have been studying and the pmcc is close to -1.
At 100cm the estimate is not reliable as we are extrapolating outside of the depths which we have been studying and we do not know if the relationship will continue beyond 48cm.
3. i) 0.526 to 3sf
ii) 0.399 to 3sf
4. a) 0.5
b) It will increase since the new entry will be ranked 6 by both. This will lead to d^2=0 and the numerator will remain unchanged, but the denominator will have increased.
5. i) a) 2
b) 0.667cm to 3sf
ii) (0.5,0), (3.5,6), (6.5,15) (I think these last two are the two they'll be looking for, but hopefully they'll be lenient as it's badly worded).
iii) a) 5.43, 3.08 to 3 sf
b) They are only estimates as they are based on a small sample size.
6. i) V as each probability is less than the previous one (although this is impossible since P(X=0) should be 0)
ii) Y as it is a perfectly symmetrical which increases to a common mode, mean and median and then decreases
7. i) Geometric with p=0.6, assuming that the probability of an arrival of a woman is independent of previous arrivals, that this probability is constant for all arrivals and that we can classify each arrival as being either female or male.
ii) 0.0383
iii) 0.064
8. i) 0.0352 to 3sf
ii) a) 0.168 to 3sf
b) 0.416 to 3sf
9. i) a) 3024
b) 1680
ii) a) 5/14=0.357 to 3sf
b) 1/63 = 0.0159 to 3sf
Let me know if you disagree with any. I often make calculator errors on S1.

i would have said its because we dont know true values (thats whats usually on markschemes),
also for cum frequency, the first would be (0,0) ormaybe (-0.5, 0) even thought it doesnt make sense, because 0 wasnt a group so you dont have to use true group boundaries

anyone remember how many marks 9biia, the 5/14 one, was out of?

What is this about the fact that the 5 graph things where u had to choose which was geometric etc being wrong, they might be handing all the marks to people because they all had 0's but geometric cant have 0.. anyone else heard about this ?

I'm sure! Hope to see you on here on the 8th March. Ultimately having to resit this, or any other module for me, would be mad! Already got 6 initial exams lined up for June, inc. C3, C4 and M1 (doing Maths A level in a year) - I think any more maths would be the death of me!

I have 6 as well without resits. C4, M2, FP2, D1, PH5 and MU6 :P - the last 2 being physics and music. That's discounting all the pracs :L