Suppose you take a deck of cards, toss it in the air, and note how everything falls.
You analyze the order, left to right, of how the cards fell. You note how many were face down, face up, and skewed at various angles. You note exactly the degree to which some cards overlap others.
Then you get out a calculator (actually, you might need a high powered computer), and calculate the weight of the cards, wind velocities, and card aerodynamics. You do a lot of very impressive research.
Then you come out and say something like, “The odds against the cards falling this exact way is 7.6 x 10^87 to one. This means I could toss cards up in the air once every second for 4 million times longer than the scientist says the universe is old, and still never get this combination.
"It is is obviously ridiculous to believe that this happened by mere chance, but it’s what the SCIENTISTS want you to believe. It is obvious to anyone with a brain that God must have done it!"
And yeah, many Intelligent Design arguments and Creationist arguments involving math involve exactly this kind of calculation.
In case it isn’t obvious, let me spell out what is wrong with this argument. When you tossed the cards in the air, they HAD to come down in some configuration. One to One probability.
What the Creationist has done is taken all the factors and tried to predict the odds of this particular configuration of cards coming down in this specific way before it happened. While this is a good way of coming up with very large improbabilities, the only way the number has any meaning is if you take the same deck of cards, shuffle ‘em up, toss them in the air again, and have all the cards fall EXACTLY the same way as they did the first time. The probability of that happening may have some relation to what the Creationist has come up with.
Similar arguments are used in abiogenesis, but really, there is so much that is unknown about the chemical reactions that may have given rise to life on this planet that trying to use any numerical calculations of odds is a meaningless exercise. Using the above argument, with abiogenesis we don’t know the wind velocity, the weight of the cards, or many of the factors that determine how the cards will fall. So the Creationist uses simple-minded estimations do calculate the odds; estimations deliberately designed to make the odds seem lower.
So, beware when the Creationist or Intelligent Design push numerical improbability at you. While this may not be an exact analogy in every case, it certainly is in many.