2011 UNCO Math Contest II Answer Key
4) (a) (b)
8) (a) (b)
9) (a) (b)
10) First try for . The crossing off process yields each one being one less than a factorial. So for general you should end up with. Now look at again and replace with (order does not matter). Crossing off gives you reminding one of the coefficients in Now let , and watch what happens remember that . There are other approaches.
11) See solution to #2. Integers that are one less than a prime cannot be written in the form .