How do you calculate experimental uncertainty using the Gaussian formula?

[raintrek]

Homework Statement

 

[Mr.Brown]

erm the general idea is right but i guess your derivatives are wrong :)

you should get
ΔN = sqrt [ ( (-a/y)*exp(-x/y)*Δx )² + ( (ax/y²)*exp(-x/y)*Δy )² ]

y and x interchanged in first term :)

i hope that solves your problem otherwise i don´t know what´s wrong there the gauß formula is ok as far as i see :)