A population of middle school students contains 160 sixth graders, 180 seventh graders, and 140 eighth graders. Nine seventh graders were part of a random sample of the population chosen to participate in a survey. For the sample to accurately represent the population, about how many sixth graders should be chosen?

The sample should include the same proportion of sixth graders as seventh graders. Since 9 out of 180 seventh graders were sampled, the sampling rate is 9 ÷ 180 = 0.05. Applying that rate to 160 sixth graders gives 160 × 0.05 = 8, so about 8 sixth graders should be chosen.

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