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Editor's note: The following are questions received from viewers of "Mad Money," seen every day at 6 p.m. EDT on CNBC.

How can a stock like Dell (DELL) - Get Free Report come out with a bad number after the close and drop like a lead weight before the 9:30 a.m. stock market open? Ruth from Texas

James J. Cramer:

Investors may trade in the after-hours markets in the morning from 8:00 a.m. to 9:30 a.m. and in the afternoon from 4:00 p.m. to 6:30 p.m. Most traditional and discount brokers allow individuals to trade outside of normal market hours. But, keep in mind that the market is generally much less liquid during these times, and some firms may charge a higher commission.

Want more Cramer? Check out Jim's rules and commandments for investing from his latest book by

clicking here