720
Explanation: If you were to choose a random poster to place first, you have 6 different posters you can place there. When you go to place the second poster, you have 5 posters you could pick. This pattern keeps going until you only have one poster. To show this in a mathematical way; 6 x 5 x 4 x 3 x 2 x 1 (You always multiply your different choices). Another way this same thing could be expressed is 6! — with the explanation point being called a radical sign. It simply means to multiply the number by any whole number that comes before it but doesn’t go past 1.