muti question stats

The # of tow phone call requests coming into an tow truck station on Tuesday (between 7:00 - 8:00 AM) has a probability dist. With a mean of four.
i) State what type of prob. Dist. would be appropriate for this.
ii) Find what’s the prob. of not getting any emergency tow calls between 7-8 a.m.
iii) Find the prob. of receiving 5 emergency tow calls between 7-8 a.m.
iv) List what is the # of emergency tow calls expected to be received.
v) List what is the std. dev. of emergency tow calls received.

orendacl said:

The # of tow phone call requests coming into an tow truck station on Tuesday (between 7:00 - 8:00 AM) has a probability dist. With a mean of four.
i) State what type of prob. Dist. would be appropriate for this.
ii) Find what’s the prob. of not getting any emergency tow calls between 7-8 a.m.
iii) Find the prob. of receiving 5 emergency tow calls between 7-8 a.m.
iv) List what is the # of emergency tow calls expected to be received.
v) List what is the std. dev. of emergency tow calls received.

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Please share your work with us, indicating exactly where you are stuck - so that we may know where to begin to help you.

Well, I think this is a Poisson for the first answer.
But...Next queston is:
I was gone for an entire week and missed in class material.
I have a TI-89 calculator (titanium model) where the instructor apparently showed how to input these. How do you set up the first problem?
Example:
For the first one I coem up with u=4;P(x<=0)= ... but not sure how to enter this in my calc.

Please advise.
Thanks!

One more thing. The TI has a menu for stats, and in it I find poisson pdf.
Would the .u, value be 4, the x value be zero (in this case)... with that I get 1.48 as an answer that cannot possibly be the probability of not getting any calls. Just need to know how to properly inout these I think. It seems that the subsequent ones should be farily easy if I can get on track with the method on the first - thanks.

I couldn't help you with that - I do not have that calculator.

You may want to goto TI web site and look - I heard that site is very helpful.

It's actually my dad's calculator, and in my high school math we won't be able to use this calculator on tests anyhow. Does anyone know how to do this problem showing wor and using a basic scientific calculator?
By showing work, I do not mean solving the entire problem...just what formula to use. Answers do not do me any good as I do not know how to do the problem then.

orendacl said:

The # of tow phone call requests coming into an tow truck station on Tuesday (between 7:00 - 8:00 AM) has a probability dist. With a mean of four.

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i) State what type of prob. Dist. would be appropriate for this.

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Yes, it is a Poisson. \(\displaystyle P(X)=\frac{{\lambda}^{x}\cdot e^{\lambda}}{x!}\)

ii) Find what’s the prob. of not getting any emergency tow calls between 7-8 a.m.

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Go to the Poisson pdf menu in the Stats section of your TI89, enter in \(\displaystyle {\lambda}=4, \;\ X=0\)

Use Poisson cdf if you have to sum. Say, they want the probability that between 4 and 8 calls will be recived between 7 and 8 am.

Same as \(\displaystyle P(0)=\frac{(4)^{0}\cdot e^{-4}}{0!}=e^{-4}\approx .018\).

iii) Find the prob. of receiving 5 emergency tow calls between 7-8 a.m.

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\(\displaystyle {\lambda}=4, \;\ X=5\)

iv) List what is the # of emergency tow calls expected to be received.

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The expected value (mean)and variance of a Poisson are, respectively, \(\displaystyle {\mu}={\lambda}, \;\ {\sigma}^{2}={\lambda}\)

v) List what is the std. dev. of emergency tow calls received.

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Square root of the variance.