In order to obtain a sample of voters in pennsylvania, a simple random sample of 10 counties is selected. from each of the selected counties, 10 precincts are chosen at random. finally, from each of these 100 precincts , a simple random sample of 20 voters students is selected. thus, the final sample consists of 2,000 voters.
this is an example of which type of sampling strategy? a) simple random samplingb) stratified samplingc) multistage samplingd) convenience sampling

In statistics, there are several strategies to select a sample. Remember that a sample is a sub group selected from a population. This sample selection must be random to have more reliability in the research, each answer option represents a type of sampling.

In this case, the researcher is using a multistage sampling, because it consists  in taking smaller sample units at each stage, which is being done in this example. First, is selected a number of counties, then the precincts, and at the end the voters. By this way, the sample is being reduced to less subjects at each stage.