(Sirius XM story updated with stock closing price and additional look at Sirius XM's stock price and volume increases)NEW YORK ( TheStreet) -- Sirius XM ( SIRI) stock finished Monday's trading session up about 4% to 86 cents after sliding 3.1% to 80 cents Monday morning. Sirius XM stock had been trading at above-average volumes. More than 159 million shares were trading hands Monday early afternoon, compared with the average three-month volume of 90.1 million shares. Many market observers believe the rise in volume had much to do with the addition of Sirius XM to the NASDAQ Q-50 Index, effective at the market open Monday. The purpose of the NASDAQ Q-50 Index is to track the performance of the 50 securities that are next in line to replace the securities currently on the NASDAQ-100 Index.
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