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# S2 problem question Watch

1. It is part C in which I am struggling with - I have looked on the tables for p(x<= 10) for the last value in which it is greater than 0.9, I found this value, but then the final answer on the markscheme correlates to a different value?

Thank you
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2. (Original post by iMacJack)
It is part C in which I am struggling with - I have looked on the tables for p(x<= 10) for the last value in which it is greater than 0.9, I found this value, but then the final answer on the markscheme correlates to a different value?

Thank you
Look at the percentage points table, i.e: the table right below the normal distribution one in your formula booklet, you'll see that it gives a z value of 1.2816.
3. (Original post by Zacken)
Look at the percentage points table, i.e: the table right below the normal distribution one in your formula booklet, you'll see that it gives a z value of 1.2816.
I don't really see how this is helping me
4. (Original post by iMacJack)
I don't really see how this is helping me
Oh, sorry. I assumed it was a normal distribution question without looking at the previous parts.

. Now look in the x=10 row of your poisson table.
5. (Original post by Zacken)
Oh, sorry. I assumed it was a normal distribution question without looking at the previous parts.

.
According to the markscheme, apparently not
6. (Original post by iMacJack)
According to the markscheme, apparently not
Does this help:
7. (Original post by Zacken)
Does this help:
Yeah - they were the two values I found, but then in the markscheme the final answer is lambda = 7/4?
8. (Original post by iMacJack)
Yeah - they were the two values I found, but then in the markscheme the final answer is lambda = 7/4?
Yes, because Charlotte does it over 4 hours. So, really what you've found is where .

But the random variable is over 1 hour. So , that is: .
9. (Original post by Zacken)
Yes, because Charlotte does it over 4 hours. So, really what you've found is where .

But the random variable is over 1 hour. So , that is: .
Oh yeah... should've realised that

Thank you
10. (Original post by iMacJack)
Oh yeah... should've realised that

Thank you
No problem.

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