Modern PCs may have evolved from simple calculating machines, but you wouldn't necessarily know it by looking at the latest version of Microsoft Excel. According to a post on the Microsoft Developer Network's Excel blog, the spreadsheet application gives erroneous results for 12 basic multiplication operations that a pocket calculator could handle flawlessly. Those operations include 7.1*850, 5.1*12850, 10.2*6425, 20.4*3212.5, and a few others that add up to either 65,535 or 65,536. In those cases, Excel erroneously returns a result of 100,000.
The blog post doesn't elaborate on the cause of the bug, simply stating, "This issue was introduced when we were making changes to the Excel calculation logic in the Office 2007 time frame." However, Microsoft is reportedly working on a fix, and that fix is expected to make it through the company's build lab and onto a download site "very soon." A link will show up on the blog when the fix is rolled out.