Suppose economists develop an economic model and find that "it works great in theory, but it fails in practice." which of the following should the economists do next?
a. they should retest the current model, as there may have been an error in the testing methods the first time.
b. they should revise the model in light of its failure to explain or predict real world events.
c. they should leave the model as is. a model does not need to explain or predict real world events.
d. none of the above.

Asupermarket has been experiencing long lines during peak periods of the day. the problem is noticeably worse on certain days of the week, and the peak periods are sometimes different according to the day of the week. there are usually enough workers on the job to open all cash registers. the problem is knowing when to call some of the workers stocking shelves up to the front to work the checkout counters. how might decision models the supermarket? what data would be needed to develop these models?