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    Dividing people into groups

    How many options are there for 25 students to divide into groups of 3,4,5 and 6? My solution was 25C6 x 19C5 x 14C4 x 10C3 / 4! but not sure if right or wrong. Someone please clarify.
  2. S

    Divisibility Induction

    Prove for n>0, 7^n +3n(7^n) - 1 is a multiple of 9
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    How many terms

    3^n - 3^n+1 + 3^n+2 - 3^n+3 +...+ 3^3n How many terms are there? The answer says 2n+1.
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