According to the Darvas Box stock trading system, a trader looks at a chart of stock prices over time and identifies box-shaped patterns. Then one buys the stock if it appears to be in the lower left corner of a box, and sells if in the upper right corner. In simulations with real data, using a sample of 376 trials, the average hold time for a stock was 41.12 days.
If the sample standard deviation was 12 days, give a 90% confidence interval for the average hold time in days.