Shell petrol station has been making average sales of 50 barrels of petrol daily. After establishment of another pump station nearby, the manager of Shell claims that their daily sales have declined. The following are daily sales for Shell during the first twelve days after the establishment of another pump station nearby: 55, 57, 49, 62, 51, 58, 57, 46, 60, 58, 53 and 52. On the basis of this sample data, analyze the claim of the manager at 5% level of significance.