The number of sit-ups that all tenth-grade girls can do in 5 minutes is normally distributed. beth surveyed 20 of her fellow intramural tennis players, all tenth-grade girls, and determined the mean number of sit-ups they could do. can she make an inference about the population mean for all tenth-grade girls based on the sample? no, because the sample size was not big enough. no, because she did not use a simple random sample. yes, because the sample size was big enough. yes, because she used a simple random sample.