Turn off a calculator
As you are finishing up your math homework, the power goes out. You realize that it might not come on for a while, so you should probably just call it quits. You reach for the calculator to turn it off, but then realize that you are not sure whether it was on or off to begin with. You know that the "on" button will turn the calculator on if it is off, but does nothing if the calculator is already on. To turn the calculator off, you must first press the "2nd" key, and then the "on" key. However, if the calculator is off, the "2nd" key has no action. Given that the calculator could be off, on, or on with the "2nd" key already pressed, is there a sequence of button presses that will guarantee the calculator is off once finished?