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Statistics Question:

Here is a Maths question from a recent mock today. Can somebody check my answers? I remember the questions.

36% of flowers grow into blue, the rest into red. There are 40 flowers in a bag.

Calculate the probability that if I take 5 bags, fewer than 2 will have more blue then red

ii) By a normal approximation, I take n balls and probability that over 244 become blue is 0.0521. Find n

My solution

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A little help please
Hmm the first part seems fine but I dont agree with your second part. I believe the value should've been 243.5 instead of 244.5.
Actually never mind it says over 244 so 244.5 is correct. Yup everything looks correct.
Original post by Radioactivedecay
Actually never mind it says over 244 so 244.5 is correct. Yup everything looks correct.


Are both values correct? Can you check? I rounded earlier in my ii) but got 738 nonetheless.
Original post by thekidwhogames
Are both values correct? Can you check? I rounded earlier in my ii) but got 738 nonetheless.


Not sure bout the last bit tbh cuz how did u get a polynomial in terms of n squared when it should've been in terms of n and root n?
Original post by Radioactivedecay
Not sure bout the last bit tbh cuz how did u get a polynomial in terms of n squared when it should've been in terms of n and root n?


I standardised and then multiplied both sides and squared, sorry I didn't explain that. This was in my applied mock year 2 today and I rushed it so I want to know if it's correct :tongue:
Original post by thekidwhogames
I standardised and then multiplied both sides and squared, sorry I didn't explain that. This was in my applied mock year 2 today and I rushed it so I want to know if it's correct :tongue:


It should be right if you were accurate cuz the answer is definitely close to 27 squared.
Original post by Radioactivedecay
It should be right if you were accurate cuz the answer is definitely close to 27 squared.


Can you try it yourself and check please? Sorry i'm asking too much just paranoid :tongue:
Bump
Original post by thekidwhogames
Are both values correct? Can you check? I rounded earlier in my ii) but got 738 nonetheless.


Sorry bout that I fell asleep. I did it and 738 was indeed one of my answers, but may I ask why you disregarded the other asnwer, as there doesn't seem to be a criteria that helps me eliminate one of the answers?
Original post by Radioactivedecay
Sorry bout that I fell asleep. I did it and 738 was indeed one of my answers, but may I ask why you disregarded the other asnwer, as there doesn't seem to be a criteria that helps me eliminate one of the answers?


I think the other was 625. I disregarded it as the question asked to find the value of n so I assumed one. Do I lose marks?
Original post by thekidwhogames
I think the other was 625. I disregarded it as the question asked to find the value of n so I assumed one. Do I lose marks?


This is a weird one, either the mark scheme allows both answers or there must have been a tiny detail to help you choose the right answer that you overlooked. Either way I'm not sure cuz from what I can see both answers seem valid but I think you'll probably get the marks dw.
Original post by Radioactivedecay
This is a weird one, either the mark scheme allows both answers or there must have been a tiny detail to help you choose the right answer that you overlooked. Either way I'm not sure cuz from what I can see both answers seem valid but I think you'll probably get the marks dw.


It just said he picked n balls and probability that over 244 became blue was 0.0521; find n

Would I lose a mark or 2?
I woulda thought for the first part you want 1-P(X<21) = 0.02400. The way you've done it to me seems like you still take into account 20 flowers being blue but you want more blue flowers than red. I haven't gone over stats in a while so could be wrong tho
Original post by number0
I woulda thought for the first part you want 1-P(X<21) = 0.02400. The way you've done it to me seems like you still take into account 20 flowers being blue but you want more blue flowers than red. I haven't gone over stats in a while so could be wrong tho


I thought for binomial distribution since it's not continous like the normal; p(x>20) = 1-p(x<=19)
Original post by thekidwhogames
It just said he picked n balls and probability that over 244 became blue was 0.0521; find n

Would I lose a mark or 2?

I plugged both answers into an online normal distribution calculator and only the 625 answer worked, giving me a porbabilty of being more than 244.5 of 0.0521, whereas the other answer, 738, gave me a probability of being LESS than 244.5 of 0.0521. I will not pretend to know why this but I'm tagging someone who can hopefully explain for the both of us:

@RDKGames
Original post by thekidwhogames
I thought for binomial distribution since it's not continous like the normal; p(x>20) = 1-p(x<=19)


I think its P(x=>21) = 1 - p(x<=20) is the way I'd look at it
Original post by Radioactivedecay
I plugged both answers into an online normal distribution calculator and only the 625 answer worked, giving me a porbabilty of being more than 244.5 of 0.0521, whereas the other answer, 738, gave me a probability of being LESS than 244.5 of 0.0521. I will not pretend to know why this but I'm tagging someone who can hopefully explain for the both of us:

@RDKGames


I'm a bit lost; I applied the normal approximation and standaridsed and used inverse normal function to find z then do it?

Thanks for the tag
Original post by number0
I think its P(x=>21) = 1 - p(x<=20) is the way I'd look at it


Now I'm starting to think I should've not rushed it :frown:

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