Ask Marilyn: Taking Issue with the Triplet Question

Vance Fisher of Haddam Neck, Connecticut, writes:

Marilyn: I vote for the reader! He posed a gender question regarding his future grandchildren. (July 29, 2012) You seem to have addressed it as a birth order question (you called the babies 1, 2, and 3). Triplets can be three girls, three boys, two girls and a boy, or two boys and a girl. Considering gender and nothing else, there are only four scenarios possible, or 25 percent.

Marilyn responds:

The original answer is correct. Only four scenarios are possible, all right, but the chances of getting them differ. I called the babies 1, 2, and 3 to give them a gender-free label, not to indicate birth order. Instead, let's call them Munchkin, Pumpkin, and Peanut. These are the gender possibilities:

Boy Munchkin, Boy Pumpkin, and Boy Peanut (three boys)
Boy Munchkin, Boy Pumpkin, and Girl Peanut (two boys and a girl)
Boy Munchkin, Girl Pumpkin, and Boy Peanut (two boys and a girl)
Girl Munchkin, Boy Pumpkin, and Boy Peanut (two boys and a girl)
Boy Munchkin, Girl Pumpkin, and Girl Peanut (two girls and a boy)
Girl Munchkin, Boy Pumpkin, and Girl Peanut (two girls and a boy)
Girl Munchkin, Girl Pumpkin, and Boy Peanut (two girls and a boy)
Girl Munchkin, Girl Pumpkin, and Girl Peanut (three girls)

So the chances of three boys are 1/8, the chances of three girls are 1/8, the chances of two boys and a girl are 3/8, and the chances of two girls and a boy are 3/8.