Explanation:
There are 8 letters in the word "GEOMETRY".
Use the nPr permutation formula with n = 8 and r = 7 and you'll find that 8P7 = 40320.
Or you can compute it like this 8*7*6*5*4*3*2 = 40320
This would be the answer if we could tell the E's apart.
However, we cannot tell the E's apart, so we have to divide by 2 to correct for the double-counting.
There are 40320/2 = 20160 different seven letter combinations possible.
