The article discusses how scientists test a hypothesis about the average of a group. They use statistical methods like the z test and t test to decide if the hypothesis should be rejected. If the sample average is very different from the expected average, the hypothesis is rejected. Making mistakes in this process can happen, like rejecting a true hypothesis or not rejecting a false one. The t test is used when the sample size is small. The article explains the rules for these tests and how they help researchers make conclusions about their data.