ve that the average attention span of a teenager has dropped in recent years. They estimate that in 2000 a teenager could concentrate on something for about 2.5hrs, with a standard deviation of 30 minutes. The group finds a large number of identical teenagers from 2020, all of whom have an attention span of 80 minutes. What is the minimum number they would need to include in a survey to be able to conclude that attention spans had gotten shorter at the: (a) 10% sig level? (b) 5% sig level? (c) 1% sig level