How did she know While a red mark was placed on the forehead of each of three blindfolded women seated facing each other in a circle they were told that the the mark might be either red or White Upon?

Answer 1

If hers was white, then one of the other 2 women with Red dots would have known their color. The way they would have known is .... each of them would be seeing 1 Red and 1 White which means they cannot be White since all 3 raised their hands, and would have guessed their color to be Red, but they did not. This way she derives that hers cannot be White, and only can be RED!