made with the foreknowledge
of at least one of the key elements
Imagine you are driving in a car, and wonder if the light will change before you reach it. If you know any of the following, you can make an educated guess: the speed of your car, distance to the light, period of each of the light's color cycle.
Keep in mind that an educated guess is only as good as the information behind it. While it can be superior to a naked guess, erroneous information can produce wildly inaccurate results far beyond any reasonable scale of magnitude because any mistakes made are amplified by the guessing process.
Remember...for any question there is usually only one right answer. There are, however, infinity-1 wrong answers.