According to the national bridge inspection standards (nbis), public bridges over 20 feet in length must be inspected and rated every 2 years. the nbis rating scale ranges from 0 (poorest rating) to 9 (highest rating). university of colorado engineers used a probabilistic model to forecast the inspection ratings of all major bridges in denver. (journal of performance of constructed facilities, feb. 2005.) for the year 2020, the engineers forecast that 9% of all major denver bridges will have ratings of 4 or below. use the forecast to find the probability that in a random sample of 10 major denver bridges, at least 3 will have an inspection rating of 4 or below in 2020.