For a daily airline flight between two cities, the number of pieces of checked luggage has a mean of 380 and a standard deviation of 20. on what percent of the flights would you expect from 340 to 420 pieces of checked luggage?

340 is (340-380)/20=-2, or 2 standard deviations below the mean.
420 is (420-380)/20=2, or 2 standard deviations below the mean.

 95% of values lie within 2 standard deviations of the mean, so the answer is 95%.

this is a good question! i'll do some research and come back when i have the answer!