Why Warren wants Walmart

Warren Buffett is doubling up on Wal-Mart Stores Inc. (WMT) stock. Why does Warren want Walmart? Obviously, he thinks the price will go up from the $49.81 at which I estimate he bought the shares. But the stock is not cheap -- unless Warren has a better yardstick for measuring Walmart's future earnings growth.

How much Walmart stock does Buffett own? CNNMoney reports that his investing company, Berkshire Hathaway (BRK.A), boosted its stake by 90% from 19.9 million in the second quarter to 37.8 million shares in the third quarter. I don't know precisely what price he paid for the 17.9 million additional shares he bought , but Walmart's stock ranged between $47.73 and $51.88 in the third quarter, so let's guess his average cost was halfway in between: $49.81.