TV’s Barnaby Jones debuted on this day in 1973 where Buddy Ebson solved many big mysteries. But if you’re wondering how long it’ll take to double your money at various rates of interest, you don’t have to hire someone like Barnaby Jones. How long will it take at 8 percent, or 11 percent, or 5? Just divide the rate of interest into 72. If your money is earning 8 percent, dividing that into 72 gives you 9. Meaning with the interest compounded annually, your money will double in only 9 years. At 12 percent, using our “rule of 72”, you find it takes only 6 years to double. Try it on your working investments and see how long it will take to “double your pleasure, double your fun”! And that's the On The House tip for today...