“Let’s Make a Deal.” Marilyn vos Savant, who is listed in the Guinness Book of World Records Hall of Fame as having the “Highest IQ,” writes a weekly column in the Sunday newspaper supplement Parade Magazine. Her column, “Ask Marilyn,” is devoted to games of skill, puzzles, and mind-bending riddles. In one issue (Parade Magazine, Feb. 24, 1991), vos Savant posed the following question:

Suppose you’re on a game show and you’re given a choice of three doors. Behind one door is a car; behind the others, goats. You pick a door—say, #1—and the host, who knows what’s behind the doors, opens another door—say

#3—which has a goat. He then says to you, “Do you want to pick door #2?” Is it to your advantage to switch your choice?

Marilyn’s answer: “Yes, you should switch. The first door has a 13 chance of winning [the car], but the second has a 23 chance [of winning the car].” Predictably, vos Savant’s surprising answer elicited thousands of critical letters, many of them from Ph.D. mathematicians, that disagreed with her. Who is correct, the Ph.D.s or Marilyn?