(Over)Night Moves

QHow can a stock suddenly start trading at a very different price than where it closed the day before? — V.B., Winona, Minnesota

AIt means that something happened overnight while the market was closed. Imagine that shares of Help Depot (ticker: RUOK) are trading around $75 per share when the market closes. If the company then reports blowout revenue and earnings, demand for the shares may build up. When stock trading resumes the next morning, the stock price probably won’t open at $75 and then rise gradually. Instead, it’s likely to just begin trading at a significantly higher level. That’s because many investors will now assign a greater value to the company, and the limited existing shares will have risen in value to meet the higher demand. Buyers are simply willing to pay more for the shares. The opposite can happen, too, of course, if there are negative developments about a company.

QWhat’s a mock portfolio? — H.K., Jacksonville, Florida

Amock portfolio is a pretend one — ideal for beginning investors, and others who want to practice investing without putting any real money down. You can set one up on paper, or you can create an online portfolio at sites such as Finance.Yahoo. com. Then go through the motions of investing: Study companies, decide which ones to invest in, note that you’ve “bought” a certain number of shares at a certain price, and then follow the progress of the companies and the stocks. Over time, see how you do. A mock portfolio can serve as a kind of watch list, too, as it can alert you when the price of a stock you’re interested in falls to an attractive level.