If the constant of proportionality of "y = x" is 1, meaning the ratio between x and y (and vice-versa) is always equivalent to 1, does that mean that for x equal to zero and y equal to zero, the ratio will still be 1?

Suppose that 3% of all athletes are using the endurance-enhancing hormone epo (you should be able to simply compute the percentage of all athletes that are not using epo). for our purposes, a “positive” test result is one that indicates presence of epo in an athlete’s bloodstream. the probability of a positive result, given the presence of epo is .99. the probability of a negative result, when epo is not present, is .90. what is the probability that a randomly selected athlete tests positive for epo? 0.0297