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# S2 Edexcel Today Question watch

1. Okay the other threads getting way too big and with the server the way it is its impossible to post in there.

My friend was asking me about the question where you had to approximate the B(100, 0.1). I used a Poission, but he said he used the normal approximation, both should work as the values of n, p, np and nq, satisfy them, do you think either of us will lose marks for using the approximation we did? It said to use a suitable approximation.

2. I used a poisson aproximation X~B(100,0.1) : Y~Po(10)

I beleive that using the poisson is the right aproximation, as you had to use a Normal later on to aproximate a Po(17.75)
3. i use normal but i think both is fine
4. how did u work out the median?

this is wot i did:

f(x) = 1/3 0<=x<1
= 8x^(3)/45 1<=x<=2
= 0 elsewhere

the median will be in the second bit

so integrate with limits m and 1 making it equal to a half

rearrange to make x subject

and you should get a quartic root

someone validate me
5. My immediate thought was to use the Normal approximation because they asked you how to find the mean and the variance in the question before that. But when i thought about it, it seemed so much easier to use Po(10) approximation.
6. for the last question F(x) i mistakingly put -13/45 instead of plus 13/45 the question was out of 7 and up till that point it was ok so how many marks would i expect to get?

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