A quality control engineer at a potato chip company tests the bag-filling machine by weighing bags of potato chips. Not every bag contains exactly the same weight. But if more than 15% of bags are overfilled, then they stop production to fix the machine.

They define overfilled to be more than 1 ounce above the weight on the package. The engineer weighs 100 bags and finds that 21 of them are overfilled.

He plans to test the hypotheses: H0: p = 0.15 versus Ha: p > 0.15 (where p is the true proportion of overfilled bags).

What is the test statistic?

1. Z = 1.68
2. Z = -1.68
3. Z = 4
4. Z = -1.47