Derek is building a "learning tower". A learning tower allows small children to help in the kitchen safely. For this project, Derek needs 13 pieces of lumber. Unfortunately, Derek knows that there is an 11% chance that a piece of lumber is unusable due to being warbed, split, or having too many knots. To account for potentially unusable lumber, Derek purchases 16 pieces of lumber. What is the standard deviation of unusable board when 16 boards are purchased