Poisson distribution.. Calculator :(

Drakares

I'm on my 3rd calculator trying to figure this out :mad:

It's a SHARP EL-531RH.

[Individual wafers are known to have on average 2 scratches, calculate the probability that a - wafer has 2 or more scratches, b - in a subgroup of 6 wafers, exactly 1 has 2 or more scratches]

e^ - λ x λ^r / r!

e^ - 2 x 2^0 / 0! = -1.84 which I know is incorrect
(e^-2) x (2^0) / 0! = Error 1

Any ideas, my error or what's the story with the calculator! I've went through 2 calculators and can't get it to stop spitting out errors, no matter how many ways I bracket or try to do this, I can't get it to work.

ChemHickey

Drakares wrote: »

I'm on my 3rd calculator trying to figure this out :mad:

It's a SHARP EL-531RH.

[Individual wafers are known to have on average 2 scratches, calculate the probability that a - wafer has 2 or more scratches, b - in a subgroup of 6 wafers, exactly 1 has 2 or more scratches]

e^ - λ x λ^r / r!

e^ - 2 x 2^0 / 0! = -1.84 which I know is incorrect
(e^-2) x (2^0) / 0! = Error 1

Any ideas, my error or what's the story with the calculator! I've went through 2 calculators and can't get it to stop spitting out errors, no matter how many ways I bracket or try to do this, I can't get it to work.

Maybe instead of using a calculator to write it all in, write it in easier steps first? You know 2^0 = 1 (I presume) and that e^-2 = 1/e^2 and Also that 0! = 1 too, so you could easily write it as (e^-2)x(1/1) which is the equivalent to 1/(e^2) so that's all you'd need to write into the calculator. Often it is easier to break down the sum into the simplest terms and THEN use the calculator. It'll also show the examiner you know what you're at :P

Drakares

Cheers,

I got it anyway, herp here was using -2 as in subtract 2 instead of +/- to give it it's minus value.

All sorted