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probability problem

S

Semidevil

Diamond Member
so flaws in metal produced by high temperatures occure at a rate of 1 per 10 square feet. what is the probability that there is 3 or more flaws in a 8 x 5 feet.

ok, so I know we need to use poisson disstribution on this, e^-np * np^k/k!.

howver, I dont know my np.

so 1 per 10 square feet means 1 per 10 x 10 feet....maybe we can say this is the same as .1 per 1 x 1 feet.

so how do I put this in terms of 8 x 5 feet?

 
Are you using the Miller & Miller text? It sounds like a problem I had just a couple weeks ago. I'll take a look when I get home.
 
Originally posted by: upsciLLion
Are you using the Miller & Miller text? It sounds like a problem I had just a couple weeks ago. I'll take a look when I get home.
Click to expand...

no...it's everyones favorite...Larson and Marx
 
Originally posted by: Semidevil
so flaws in metal produced by high temperatures occure at a rate of 1 per 10 square feet. what is the probability that there is 3 or more flaws in a 8 x 5 feet.

ok, so I know we need to use poisson disstribution on this, e^-np * np^k/k!.

howver, I dont know my np.

so 1 per 10 square feet means 1 per 10 x 10 feet....maybe we can say this is the same as .1 per 1 x 1 feet.

so how do I put this in terms of 8 x 5 feet?
Click to expand...

this is a poisson ratio question isnt it? i forgot how to do them!, but i could beast any probablity question only a few months ago! its amazing how quickly u forget!

Po(lambda) where Lambda = np

if u get 1 in 100 8x5 is 40 so wont it be 0.4 per 8x5?


so Po(0.4) and then crack on with what ever the formula is again is is ?^r e^-? over something (forgot if its n! or just r or r!, i have no notes with me)

please note forum doesnt like the lambda sign so those ? u see are meant to be lambda!

edit: ah found it X - Po(?) = e^-? x ?^r / r!

ok so np or ?=0.4

and you want 3 or more flaws so that means you include three which means u do this

1 - P(X less than or equal to 2)

1 - [(e^-0.4 x 0.4^0 / 0!) + (e^-0.4 x 0.4^1/1!) + (e^-0.4 x 0.4^2/2!)]

that should be it

again i could be wrong
 
Lamda increases or decreases proportionally to the amount of sheet metal. So you have lamda = (1)(8*5/10) = 4. Otherwise otispunkmeyer's example is correct.
 
Originally posted by: upsciLLion
Lamda increases or decreases proportionally to the amount of sheet metal. So you have lamda = (1)(8*5/10) = 4. Otherwise otispunkmeyer's example is correct.
Click to expand...


yeah u mention 10sq ft, im abit confused by this, i would take that as 10 and 8x5 as 40, so lambda = 4 and not 0.4

either way the method is correct
 
Originally posted by: otispunkmeyer
Originally posted by: Semidevil
so flaws in metal produced by high temperatures occure at a rate of 1 per 10 square feet. what is the probability that there is 3 or more flaws in a 8 x 5 feet.

ok, so I know we need to use poisson disstribution on this, e^-np * np^k/k!.

howver, I dont know my np.

so 1 per 10 square feet means 1 per 10 x 10 feet....maybe we can say this is the same as .1 per 1 x 1 feet.

so how do I put this in terms of 8 x 5 feet?
Click to expand...

this is a poisson ratio question isnt it? i forgot how to do them!, but i could beast any probablity question only a few months ago! its amazing how quickly u forget!

Po(lambda) where Lambda = np

if u get 1 in 100 8x5 is 40 so wont it be 0.4 per 8x5?


so Po(0.4) and then crack on with what ever the formula is again is is ?^r e^-? over something (forgot if its n! or just r or r!, i have no notes with me)

please note forum doesnt like the lambda sign so those ? u see are meant to be lambda!

edit: ah found it X - Po(?) = e^-? x ?^r / r!

ok so np or ?=0.4

and you want 3 or more flaws so that means you include three which means u do this

1 - P(X less than or equal to 2)

1 - [(e^-0.4 x 0.4^0 / 0!) + (e^-0.4 x 0.4^1/1!) + (e^-0.4 x 0.4^2/2!)]

that should be it

again i could be wrong
Click to expand...


?
 
Originally posted by: puffff
Originally posted by: otispunkmeyer
Originally posted by: Semidevil
so flaws in metal produced by high temperatures occure at a rate of 1 per 10 square feet. what is the probability that there is 3 or more flaws in a 8 x 5 feet.

ok, so I know we need to use poisson disstribution on this, e^-np * np^k/k!.

howver, I dont know my np.

so 1 per 10 square feet means 1 per 10 x 10 feet....maybe we can say this is the same as .1 per 1 x 1 feet.

so how do I put this in terms of 8 x 5 feet?
Click to expand...

this is a poisson ratio question isnt it? i forgot how to do them!, but i could beast any probablity question only a few months ago! its amazing how quickly u forget!

Po(lambda) where Lambda = np

if u get 1 in 100 8x5 is 40 so wont it be 0.4 per 8x5?


so Po(0.4) and then crack on with what ever the formula is again is is ?^r e^-? over something (forgot if its n! or just r or r!, i have no notes with me)

please note forum doesnt like the lambda sign so those ? u see are meant to be lambda!

edit: ah found it X - Po(?) = e^-? x ?^r / r!

ok so np or ?=0.4

and you want 3 or more flaws so that means you include three which means u do this

1 - P(X less than or equal to 2)

1 - [(e^-0.4 x 0.4^0 / 0!) + (e^-0.4 x 0.4^1/1!) + (e^-0.4 x 0.4^2/2!)]

that should be it

again i could be wrong
Click to expand...


?
Click to expand...


heh lol, everytime i put it in it replaced it with ?, you have skills
 
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