3. In conducting an inspection of the condition of main steel girders in several railroad bridges, an engineer believes that the mean e'ective cross section area is at least equal to 90 percent of the original cross-sectional area as indicated on the design drawings. In a survey of 12 different girders, the cross-sectional area was measured as a fraction of the \"design cross-sectional area\" at the midspan of each girder. The results were: 0.76, 0.95, 0.73, 0.82, 0.85, 0.85, 0.89, 0.91, 0.78, 0.81, 0.86, 0.87. (a) Compute the mean and standard deviation of the data given (b) Test the hypothesis that the mean ratio of the cross section area to the design cross-sectional area is larger than 0.90 per engineer's notion