[EX09-156] The water pollution readings at State Park Beach seem to be lower than that of the prior year. A sample of 12 readings (measured in coliform/100 mL) was randomly selected from the records of this year’s daily readings: 

3.5 3.9 2.8 3.1 3.1 3.4 4.8 3.22.5 3.5 4.4 3.1 Does this sample provide sufficient evidence to conclude that the mean of this year’s pollution readings is significantly lower than last year’s mean of 3.8 at the 0.05 level? Assume that all such readings have a normal distribution.