OCR A Level Mathematics B (MEI) Paper 2 (H640/02) - 11th June 2024 [Exam Chat]

guys i have a question, (from 2018 pure & stats),
I don't understand why we don't add the 5 to the variance... can someone explain this to me?
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Reply 8

juansnip3s

6

Original post by navvvv

guys i have a question, (from 2018 pure & stats),
I don't understand why we don't add the 5 to the variance... can someone explain this to me?
Screenshot 2024-06-08 at 11.13.28 PM.png

Variance is the measure of spread of data, if even single data u add 5 the spread of them will still be the same

Reply 9

Original post by juansnip3s

Variance is the measure of spread of data, if even single data u add 5 the spread of them will still be the same

ohhh right that makes sense, thanks!

Reply 10

can someone please help me with this question - for some reason I keep getting a negative variance when I put it into the equation???

Reply 11

for some reason I keep getting a minus number for my variance ??

Reply 12

Original post by nicky6099

for some reason I keep getting a minus number for my variance ??

I did it again using the last equation
x bar as 259.7058
then did 8101050.91 - (120 times mean squared) and got 7398.525 ??????????????????

Reply 13

Remaou

4

Original post by nicky6099

for some reason I keep getting a minus number for my variance ??

This is how to answer the question. use the second equation for S_xx as we have Σx and Σx² .
Σx² - (Σx)² ÷ n = S_xx
8101050.91 - (31164.7)² ÷ 120 = S_xx
S_xx = 7396.53
(1 ÷ (n-1)) * S_xx = s²
(1/119) * 7396.53 = s² = 62.155 = 62.2
square root of 62.2 is 7.89

Reply 14

Original post by Remaou

This is how to answer the question. use the second equation for S_xx as we have Σx and Σx² .
Σx² - (Σx)² ÷ n = S_xx
8101050.91 - (31164.7)² ÷ 120 = S_xx
S_xx = 7396.53
(1 ÷ (n-1)) * S_xx = s²
(1/119) * 7396.53 = s² = 62.155 = 62.2
square root of 62.2 is 7.89

BYE I didn't see the 1/n-1
Thank you so much!!!

Reply 15

Remaou

4

Original post by nicky6099

BYE I didn't see the 1/n-1
Thank you so much!!!

ah right lol. honestly alevel maths is such a pain, its always the simple bits i forget.
your welcome and good luck tomorrow!!

Reply 16

can someone please explain this to me?
Screenshot 2024-06-10 at 4.02.45 PM.png

Reply 17

Remaou

4

chance of panther being not black is 0.94, chance of a sample of panthers being not black is 0.94ⁿ as each panther is independent of each other. for this to reach the boundary with the critical it must equal k which is 0.025 in this instance.
so 0.94ⁿ = 0.025
ln(0.94ⁿ ) = ln(0.025)
nln(0.94) = ln(0.025)
n = (ln(0.025) ÷ ln(0.94))
n= 59.61
since it can't be a fraction n = 60

Reply 18

Original post by Remaou

chance of panther being not black is 0.94, chance of a sample of panthers being not black is 0.94ⁿ as each panther is independent of each other. for this to reach the boundary with the critical it must equal k which is 0.025 in this instance.
so 0.94ⁿ = 0.025
ln(0.94ⁿ ) = ln(0.025)
nln(0.94) = ln(0.025)
n = (ln(0.025) ÷ ln(0.94))
n= 59.61
since it can't be a fraction n = 60

thank you so much!

Reply 19