Millions & Billions May 6, 1999January 29, 2017 In my April 30 column I said that if Bill Gates had invested merely one-millionth of a penny at 5% a thousand years ago, he’d have had $15 billion today. Of course, he has a lot more than $15 billion, but that is not the point. The point is: Could that possibly be correct? Could I possibly have calculated that right? Sheepishly: no. Thanks to John Ebert for pointing this out. “I think you meant ONE-BILLIONTH of a penny,” John writes. And indeed he is right. I was not overestimating the power or compound interest but, rather, underestimating it — a thousand-fold. Had Bill invested the millionth-of-a-penny at 5% as I posited, he’d have $15 trillion today, which actually is more than he has — indeed, it is actually about double America’s gross domestic product. It all comes back to Mary Poppins, doesn’t it? (“When you invest . . . your . . . tuppence in the bank . . . safe . . . and . . . sound . . . Soon that tuppence . . . safely . . . invested in the bank . . . will comPOUND!”) HOW CAN YOU LEAVE THE TV ON WHEN YOU’RE NOT WATCHING IT AND WASTE PENNIES OF ELECTRICITY THAT COULD BE WORTH BILLIONS TO YOUR GREAT-GREAT-GREAT-GREAT GRANDCHILDREN? (In case you missed it, this all pretty well ties into yesterday’s column.)