step 20.52 Bad Weather, Bad Tips? As part of the study of tipping in a restaurant that we met in Example 16.3 (page 374), the psychologists also studied the size of the tip in a res- taurant when a message indicating that the next day's weather would be bad was written on the bill. Here are tips from 20 patrons, measured in percentage of the total bill:34 PS 18.0 19.1 19.2 18.8 18.4 19.0 18.5 16.1 16.8 14.0 19.4 17.0 13.6 17.5 20.0 20.2 18.8 18.0 23.2 18.2 Do the data give convincing evidence that the mean percentage tip for all patrons of this restaurant when their bill contains a message that the next day's weather will be bad is less than 20%? (Note that 20% is an of ten-recommended size for restaurant tips.)