3. elena wants to know what proportion of peo...

# Brief Explanations: Elena can use sampling. First, define a population (e.g., all residents in a city). Then, randomly select a sample from this population. For example, use a random - number generator to pick households. Next, survey the sample by asking if they have cats as pets. Finally, calculate the proportion of cat - owning households in the sample to estimate the proportion in the whole population. # Answer: Elena can use sampling: define population, randomly select sample, survey sample, calculate proportion in sample to estimate population proportion.