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Exam Hack | CIE A2 Maths | S2 | Poisson Distribution Question

🕑 Added 2022-09-20 02:56:33 +0000 UTC

Comments

Lyndon Dias

hey, Jacob, in the 23rd [a] question, you made a mistake, the answer is 0.144

Samhitha Ahoratra

Hi, don't know why in Q15 s2019_61, they used 115 as mean and standard deviation, also if i were to use 2.3, i get the z value as 71.3, which i don't think i can find on the z distribution graph. so what would i do in that case. Please try and help soon, I have my exam on Monday lol

Samhitha Ahoratra

hey, around 31:28, wasn't z already less than -0.982, so when subtracting you switched the sign, and then switched it again. I don't understand why you switched the sign the first time.

Intuitive

Maybe you should recap the S1 Normal distribution content on my Youtube. This is just to do with the symmetry of the distribution. Also watch the videos I link in the description box bellow the video.

Intuitive

Oh you're talking about continuity correction. You're plussing 0.5 for that case because > 40 needs to exclude 40 to be as accurate as possible, so you use > 40.5 not > 39.5, as 39.5 would include 40. Basically, if you're confused about this look up continuity corrections for the normal distribution approximation. I talk about it as well in my "S1 Normal Distribution - part 2" on YouTube.

Eirene Chiam

in question 4), it switches from poisson distribution to normal distribution, so in this questions the normal distribution is X~N(31, 31) since X~Po(31), and they are asking me to work out P(X>40), typically when I've seen '>' signs, I usually -0.5 from the X value (40 in this case) to plug into the equation- so i got (39.5 - 31)/square root 31, however when I checked the ms, they used 40.5 (+0.5) instead of 39.5 (-0.5) which is the value I was typically told to use and had worked for me in past questions. So now I'm unsure as to when I should be minus-ing or plus-ing the 0.5 error.

Intuitive

When would you get a mean of +/-? I can't see how that would be possible. I guess if you did you'd plug in the '+' value and the '-' value getting two different solutions when plugging it into your Poisson Density function.

Eirene Chiam

Also, having some problems with poison to normal distributionq2ii) in the worksheet as i got a negative z value and I calculated the 1- -ve z value to get the probability but when I checked the answer at the back it’s just the +ve version of the z value?

Eirene Chiam

Hi, thanks for all the great content 😊, quick question, when it switches from poison to normal and we have to +/- 0.5 to the µ, how do we know when to -0.5 and when to +0.5?