If your teacher won't let you use a calculator with combinations on it, then you might like this formula better: the number of combinations of n things taken r at a time isSo, for C(65,4), we start with 65, then come down 1 each time until we have 4 factors on top, matched by the 4 factors of 4! on the bottom: Then the 4 cancels into the 64 giving 16, The 3 cancels into the 63 giving 21, The 2 cancels into the 62 giving 31. So the answer is (65)(16)(21)(31) = 677040 Edwin