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Suppose we want to choose 6 letters, without replacement, from 9 distinct letters.
(a) If the order of the choices is not relevant, how many ways can this be done?

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(b) If the order of the choices is relevant, how many ways can this be done?

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Suppose we want to choose 66 letters, without replacement, from 99 distinct letters.\newline(a) If the order of the choices is not relevant, how many ways can this be done?\newline \square \newline(b) If the order of the choices is relevant, how many ways can this be done?\newline \square

Full solution

Q. Suppose we want to choose 66 letters, without replacement, from 99 distinct letters.\newline(a) If the order of the choices is not relevant, how many ways can this be done?\newline \square \newline(b) If the order of the choices is relevant, how many ways can this be done?\newline \square
  1. Combination Formula: To find the number of ways to choose 66 letters from 99 without considering the order (combinations), we use the combination formula:\newlineNumber of combinations=(nr)=n!r!(nr)! \text{Number of combinations} = \binom{n}{r} = \frac{n!}{r!(n-r)!} \newlinewhere n=9 n = 9 and r=6 r = 6 .\newline(96)=9!6!(96)!=9×8×73×2×1=84 \binom{9}{6} = \frac{9!}{6! \cdot (9-6)!} = \frac{9 \times 8 \times 7}{3 \times 2 \times 1} = 84
  2. Calculate Combinations: For the ordered selections (permutations), we use the permutation formula:\newlineNumber of permutations=n!(nr)! \text{Number of permutations} = \frac{n!}{(n-r)!} \newlinewhere n=9 n = 9 and r=6 r = 6 .\newline9!(96)!=9!3!=9×8×7×6×5×4=60480 \frac{9!}{(9-6)!} = \frac{9!}{3!} = 9 \times 8 \times 7 \times 6 \times 5 \times 4 = 60480

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