Mount St. Helens is an active volcano in US, which had a strong eruption on May 18, 1980. The region around the volcano became a national park in 1982. Since the eruption, the size of the fish in Spirit Lake at the bottom of the volcano seems to have increased. In 2010, a sample of 30 rainbow trouts had an average weight of 2.3 lbs and a sample standard deviation of 4 lbs. Is there significant evidence that 30 years after the eruption, the average weight of the trouts is higher than the pre-eruption average weight of 1.9 lb? (Assume that the fish weight has a normal distribution.)