The answer to the above question is as below: 1>Provided they can take off their hat, all can know the color. 2>If they are in row ??? like a line ?? if all are facing front in a row and can see each other then >>>> everyone knows the color of thei hat. 3> If they are standing on a line then its the ladt man who knows the color of his hat. Be Explicit with the question, the row thing is vague!!! make a picture and post it .