An experimenter wishes to compare the numbers of bacteria of types A and B in samples of water. A total of n independent water samples are taken, and counts are made for each sample. Let Xi denote the number of type A bacteria and Yi denote the number of type B bacteria for sample i. Assume that the two bacteria types are sparsely distributed within a water sample so that X1, X2,..., Xn and Y1, Y2,..., Yn can be considered independent random samples from Poisson distributions with means λ1 and λ2, respectively. Suggest an estimator of λ1/(λ1 +λ2). What properties does your estimator have?