The "!" denotes the factorial of the number preceeding it. It is the product of

all the integers less than the number and greater than 1. By convention we take 0!=1.

So:

20!= 1x2x3x4x5...x18x19x20

18!= 1x2x3x4x5...x18.

So:

20!/18!=(1x2x3x4x5...x18x19x20)/(1x2x3x4x5...x18)=19x20=380

RonL