The gas mileages (in miles per gallon (mpg)) of 10 randomly selected cars, both with and without a new gasoline additive, are shown. With Additive Without additive 25.7 24.9 20.0 18.8 28.4 27.7 13.7 13.0 18.8 17.8 12.5 11.3 28.4 27.8 8.1 8.2 23.1 23.1 10.4 9.9 At 5% significance level, is there enough evidence to conclude that the gasoline with additive is more effective in increasing gas mileage?