An article in the Journal of Aircraft (Vol. 23, 1986, pp. 859€“864) describes a new equivalent plate analysis method formulation that is capable of modeling aircraft structures such as cranked wing boxes and that produces results similar to the more computationally intensive finite element analysis method. Natural vibration frequencies for the cranked wing box structure are calculated using both methods, and results for the first seven natural frequencies follow:

(a) Do the data suggest that the two methods prove the same mean value for natural vibration frequency? Use a =0.05.
(b) Find a 95% confidence interval on the mean difference between the two methods.

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Equivalent Plate, Finite Element Freq. Cycle/s Cycle/s 14.76 1 14.58 2 48.52 49.10 97.22 99.99 113.99 117.53 4 181.22 174.73 6. 212.72 220.14 7. 277.38 294.80