Conclusions: In Problem 3, the order of the two kinds used to create two pairs is unimportant, while in Problem 4, we must differentiate between the kind that three cards are chosen from and the kind that two cards are chosen from. This distinction appears to be the result of the fact that the same number of cards of each kind are chosen in Problem 3, whereas this is not the case in Problem 4. Here are some related problems that also demonstrate this subtle distinction in the problems. Try to solve the two exercises here before the reading the solutions that follow.