All 7 parts are different from each other.
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If you have to use all 7 parts then:
If you mean what in math is called "combinations" (where the order doesn't matter), there's only 1 combination because any other pattern (5791psd) can just rearrange to dsp1975.
On your calculator this would be something like 7 nCr 7 or C(n,r).
If you mean what in math is called "permutations" (where the order does matter), there are 7! = 7 * 6 * 5 * 4 * 3 * 2 * 1 = 5040 permutations.
On your calculator this would be something like 7 nPr or P(n,r).
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If you don't have to use all 7 parts, then it's a more interesting problem. (adult/teacher way of saying "it's harder")
We still have the question of combinations vs. permuations, but now we have 7 possibilities (combos of length 1, 2, 3, 4, 5, 6, or 7), for a total of 14 problems to answer this version of the original problem.
I'll leave this part as an exercise for the reader. (teacher/professor way of saying "do it yourself")