Investors bet on growth on Friday, bumping up shares in two newly listed companies with strong trajectories while remaining neutral or down on two others whose prospects are murkier.

Mining giant Rio Tinto's spin-off Cloud Peak Energy Inc edged down in its debut on the New York Stock Exchange on Friday after its initial public offering fell short of expectations on concerns that the money raised in the IPO was going to its parent company rather than its own growth.

Shares in Global Defense Technology & Systems Inc which drew 74 percent of its 2008 revenue from contracts with the U.S. Department of Defense, rose slightly in early trades on the Nasdaq.

Analysts said the company could suffer if the government cuts defense budgets.

By contrast, shares in Chinese economy hotel chain 7 Days Group Holdings Ltd and on-line education company Archipelago Learning rose by double digit percentage points.

IPO investors are used to having growth, said Matt Therian, an analyst with Connecticut-based investment firm Renaissance Capital.

Cloud Peak is really tied up in coal prices. It's kind of a murkier growth outlook for this company.

Gillette, Wyoming-based Cloud Peak raised about $459 million in its IPO on Thursday, but it priced below expectations.

The U.S. coal miner's shares opened at $14.50 on the New York Stock Exchange, more than 3 percent below the IPO price and fell as much as 6.7 percent.

Cloud Peak recovered and was at $14.70 on the New York Stock Exchange, down 2 percent.

The Cloud Peak deal was really a divestiture by Rio Tinto. The cash streams in coal are predicable ... It's not a real sexy industry and it depends very much on energy prices, said Morningnotes.com founder Ben Holmes.

But investors lapped up shares in 7 Days and Archipelago Learning. 7 Days rose 15.2 percent while Archipelago Learning was up 14.2 percent.

Analysts said 7 Days and Archipelago benefited from strong growth potential.

I think investors are bullish on where this market is going, said Therian. They've gone from five hotels in 2005 to almost 300 now.

Therian said private equity-backed on-line education firm Archipelago Learning has a significant backlog of business.

Archipelago raised about $103.1 million in its IPO.

Cloud Peak is the third-largest U.S. producer of coal and owns surface mines in Wyoming and Montana but almost all of the proceeds from the Cloud Peak IPO will go to Anglo-Australian miner Rio Tinto , which will retain a 48.3 percent stake in Cloud Peak, leading to investor pushback, analysts said.

(Reporting by Phil Wahba and Clare Baldwin)