# Can someone help me with Statistics 2?Watch

#1
Hello,

Can someone check this for me, please?

In a coffee shop one in four customers asks for biscuits with coffee. Use normal distribution approximations to calculate:

1. The probability to 4 d.p., that for the first 100 customers fewer than 20 will ask for biscuits with their coffee.

My answer is 0.102, is it correct?

Thank you!

sorry if it looks a bit dodgy

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0
4 years ago
#2
(Original post by minime_w)
Hello,

Can someone check this for me, please?

In a coffee shop one in four customers asks for biscuits with coffee. Use normal distribution approximations to calculate:

1. The probability to 4 d.p., that for the first 100 customers fewer than 20 will ask for biscuits with their coffee.

My answer is 0.102, is it correct?

Thank you!

sorry if it looks a bit dodgy

Posted from TSR Mobile
Your method is correct if it were a binomial distribution being approximated but I suspect that it is the other distribution, (one in four) being the giveaway for a rate.
1
#3
(Original post by SeanFM)
Your method is correct if it were a binomial distribution being approximated but I suspect that it is the other distribution, (one in four) being the giveaway for a rate.
Hi,

How would you do it?

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0
4 years ago
#4
(Original post by minime_w)
Hi,

How would you do it?

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I would use the Poisson distribution first instead of the Binomial.
0
#5
(Original post by SeanFM)
I would use the Poisson distribution first instead of the Binomial.
How would it look like with Poisson distribution? Y~P(_)?

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0
4 years ago
#6
(Original post by minime_w)
How would it look like with Poisson distribution? Y~P(_)?

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What is the rate for 4 customers?

Then what is the rate for 100 customers?
0
#7
(Original post by SeanFM)
What is the rate for 4 customers?

Then what is the rate for 100 customers?
1/4 x 100/4?

don't get it

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0
4 years ago
#8
(Original post by minime_w)
1/4 x 100/4?

don't get it

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Hmm, not quite. To put it another way, if it's 1 in 4, how many is it in 100?
0
#9
(Original post by SeanFM)
Hmm, not quite. To put it another way, if it's 1 in 4, how many is it in 100?
Po(25)? :/

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0
4 years ago
#10
(Original post by minime_w)
Po(25)? :/

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Bingooo well done.

Now can you do the rest of the question?
0
#11
(Original post by SeanFM)
Bingooo well done.

Now can you do the rest of the question?
Yes well the first part...

Can you help me with this one as well?

The smallest value of n such that there is a probability of at least 0.98, that fewer than n of the 100 customers will ask for biscuits.

Do I just find the smallest value that is greater than 0.98 on the tables?
Like 0.9803=2.06

Thank you!!!
0
4 years ago
#12
(Original post by minime_w)
Yes well the first part...

Can you help me with this one as well?

The smallest value of n such that there is a probability of at least 0.98, that fewer than n of the 100 customers will ask for biscuits.

Do I just find the smallest value that is greater than 0.98 on the tables?
Like 0.9803=2.06

Thank you!!!
At least 0.98, so yes. How can you find n from that z value?
0
#13
(Original post by SeanFM)
At least 0.98, so yes. How can you find n from that z value?
I don't know? It said 2.06 next to 0.9803, I was hoping that was all that I needed to do .. lol
0
4 years ago
#14
(Original post by minime_w)
I don't know? It said 2.06 next to 0.9803, I was hoping that was all that I needed to do .. lol
Okey dokey.

So you know what your value of z needs to be. If P(y<n) = p(Z<2.06), what is n?
0
#15
(Original post by SeanFM)
Okey dokey.

So you know what your value of z needs to be. If P(y<n) = p(Z<2.06), what is n?

i don't know
0
4 years ago
#16
(Original post by minime_w)
i don't know
In your example, although it was binomial, you went from n=19.5 to z = -1.27.

So in the same way, but for Poisson, your n would match up to give z=2.06. Do you see why? If so, can you find n?
0
#17
(Original post by SeanFM)
In your example, although it was binomial, you went from n=19.5 to z = -1.27.

So in the same way, but for Poisson, your n would match up to give z=2.06. Do you see why? If so, can you find n?

I still don't get it

I used P(Z < x - μ / σ)

no sign of n
0
4 years ago
#18
(Original post by minime_w)
I still don't get it

I used P(Z < x - μ / σ)

no sign of n
Your n is the x value - you just need to figure out what the x is.
0
#19
(Original post by SeanFM)
Your n is the x value - you just need to figure out what the x is.
ohh, but how do I work out x?
0
4 years ago
#20
(Original post by minime_w)
ohh, but how do I work out x?
P(X<x) = P(Z < x - μ / σ)

Your z value, which is x - μ / σ, is equal to 2.06. As you know μ and σ, how do you find x?
0
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