What is the rationale for couching the question that the investigator is investigating in terms of the null hypothesis, i.e., , by disproving a negative? Show that the sum of n i.i.d. random variables...

What is the rationale for couching the question that the investigator is investigating in terms of the null hypothesis, i.e., , by disproving a negative?

Show that the sum of n i.i.d. random variables following an exponential distribution with parameter 1 follows a Gamma distribution with parameters n and 1.