. A National Institute of Health survey of 40467 U.S adults found that 3156 of them experienced at least one major depressive ep
isode in the previous year. Make a 95% confidence interval for the proportion of all U.S. adults who experienced depression in that year. (Source: https://www.nimh.nih.gov/health/statistics/major-depression)
A coin only has two sides to flip on and is equally probably flip heads or tails. If you flipped the coin 20 times you could expect to flip 10 heads and 10 tails.