in order to determine if engine oil e will improve gas mileage, a research study was conducted. from a wide range of vehicle makes, models, and model years, 400 vehicles were randomly selected. half of the vehicles were chosen at random to receive oil e, and the other half received a generic brand of oil. the resulting data showed that vehicles that received engine oil e had substantial improvements in gas mileage as compared to those that received the generic brand of engine oil. which of the following can best be concluded based on the design and results of the research?