Can waitresses increase their tips simply by introducing  themselves by name when they greet customers? A waitress collected data on two-person parties that she waited on during Sunday brunch (with a fixed price of $23.21) at a Charley Brown’s restaurant in southern California. For each party the waitress used a random mechanism to determine whether to give her name as part of her greeting or not. Then she kept track of how much the party gave for a tip at the end of their meal.
a. Is this an observational study or a randomized experiment? Explain.
b. Identify and classify the explanatory and response variables.
c. State the null and alternative hypotheses in symbols and in words for testing the waitress’ conjecture. The sample mean tip amount for the 20 parties to which the waitress gave her name was $5.44, with a standard deviation of $1.75. These statistics were $3.49 and $1.13, respectively, for the 20 parties to which the waitress did not give her name. Th e data were not strongly skewed in either group.
d. Use appropriate symbols for the six numbers reported in this paragraph.
e. Are the validity conditions met? Explain.

f. Use these summary statistics to calculate the test statistic and p-value using an appropriate theory-based test.
g. What test decision would you reach at the 0.05 significance level? Explain what this decision means in the context of this study.