Why comdoms come in boxes of 3, 6 and 12

WHY CONDOMS COME IN BOXES OF 3, 6, AND 12
A man walks into a drug store with his 8-year old son. They happen to walk by the condom display, and the boy asks, "What are these, Dad?
To which the man matter-of-factly replies, "Those are called condoms, son. Men use them to have safe sex."
"Oh I see," replied the boy pensively. Yes, I've heard of that in health class at school." He looks over the display and picks up a package of 3 and asks, "Why are there 3 in this package?"
The dad replies, "Those are for high school boys, ONE for Friday, ONE for Saturday, and ONE for Sunday."
"Cool" says the boy. He notices a 6 pack and asks, "Then who are these for?"
"Those are for college men," the dad answers, TWO for Friday, TWO for Saturday, and TWO for Sunday."
"WOW!" exclaimed the boy, " then who uses THESE?" he asks, picking up a 12 pack.
With a sigh and a tear in his eye, the dad replied, "Those are for married men. ONE for January, ONE for February, ONE for March" . . .