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 10% of bags are over-filled then they stop production to fix the machine. They define over-filled to be more than 1 ounce above the weight on the package.

The engineer weighs 124 bags and finds that 18 of them are over-filled. He plans to test the hypotheses H0: p = 0.1 versus Ha: p > 0.1. What is the test statistic?