Two Probability question

Sandals

Note these are q's from past exam papers I am studying, so if you think I am cheating on homework just use different numbers if thats possible

Hi the first one is this;

"People arrie at an Atm at a rate of 120 per hour Whats the probability that less than 3 arrive in a given two minute interval."

My understanding 120 per hour = 2 per minute therefore less than 3 is 100% probable.

q.2 If x is normally sistributed with mean 100 and standard deviation 8 find
p(90<=x<=112)

Sandals

bump, please?? the exam in question is tomorrow.,

Caryatnid

Sandals wrote:

My understanding 120 per hour = 2 per minute therefore less than 3 is 100% probable.

Think about real life, and you wouldn't make the above wrong assumption. If you talk to 24 people in one day, it doesn't mean that you stayed awake for 24 hours and spoke to a different person each hour. Similarly, the 120 people who arrived at the ATM didn't necessarily arrive at equally spaced intervals. For example, if there was even one minute where nobody arrived at the ATM, then there has to be at least one other minute where at least three people arrived.

Teg Veece

I know this post is late but better late than never.
I had an exam in something similar last year. The way your going about it is wrong. From what I can remember, you have to use the normal distribution chart. You have to somehow normalise the event numbers and apply it too the table. Sorry, can't remember exactly what you have to do coz it's so long ago but at least that should put you on the right track....

D-Generate

For the first one isn't it to do wiht the Poisson Distribution for x=0, x=1 and x=3 and add them all together or something?

Second one is to do wiht teh normal distribution tables.