Last Week's Biggest Stock Movers: Kraft, Sonus' 44% Change

Plenty of stocks go up and down in any given week. The gainers inspire us to keep investing. The decliners keep greed in check while reminding us about the risks of the equity markets.

Let's go over some of last week's best and worst performers.

Kraft Foods (KRFT) -- Up 44 percent last week

%VIRTUAL-WSSCourseInline-742%Even blue chips can get bought out. Shares of food giant Kraft soared after the company came to terms on a deal that will combine it with ketchup giant Heinz. Billionaire Warren Buffett and Brazilian private equity firm 3G Capital teamed up to buy Heinz two years ago, and now they are joining forces to bring Kraft into the fold. The merger will create America's third-largest food company.

Stamps.com (STMP) -- Up 15 percent last week

Shares of Stamps.com moved higher after it announced that it would acquire Newell Rubbermaid's Endicia subsidiary in a $215 million deal. Endicia helps companies run their shipping operations with solutions that work seamlessly with the U.S. Postal Service.

Endicia earned just $59 million in revenue last year. However, investors see the potential in the combination with Stamps.com.

Five Below (FIVE) -- Up 11 percent last week

The fast-growing discounter selling wares for $5 or less moved up after a strong quarterly report. Net sales climbed 24 percent, as brisk expansion and positive comparable-store sales pushed Five Below's top line higher. Earnings grew even faster.

Five Below has made discounting cool, wooing young shoppers by stocking clothing, stationery items and even consumer electronics accessories priced at no more than five bucks. There's plenty of room to grow for the 366-store chain, and Five Below expects to open another 70 locations this new fiscal year.

Sonus Networks (SONS) -- Down 44 percent last week

Nasdaq's biggest loser was Sonus Networks, taking a big hit after a shocking financial update. The provider of enterprise communications solutions warned that it will post just $47 million to $50 million in revenue for the quarter that ended on Friday. Its previous guidance was for $74 million. It will also post a large quarterly deficit, reversing its outlook for a small profit during the period.

Apollo Education Group (APOL) -- Down 31 percent last week

Students continue to migrate away from the University of Phoenix. Apollo Education Group -- the parent company of the well-known but struggling for-profit university -- surrendered nearly a third of its value after another rough quarter.

New student enrollments have slipped 13 percent over the past year. Online hiccups have hurt its operations, but Web-based post-secondary educators in general have been struggling to draw students despite the advantages of Internet-based learning.

Weight Watchers (WTW) -- Down 14 percent last week

The weight loss continues at Weight Watchers. The stock has posted double-digit percentage declines in four of the past five weeks, shedding 61 percent of its value in that time.

Things started going downhill at Weight Watchers after it posted a steep plunge in subscribers during last month's quarterly report. Analysts have turned their backs on the diet management specialist, and the market has naturally followed suit.

Motley Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool recommends Five Below and Stamps.com. The Motley Fool is short Five Below. Try any of our Foolish newsletter services free for 30 days. Check out our free report on one great stock to buy for 2015 and beyond.