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Santa Clara, California, United States
24 = 7+7+5+5
25 = 5+5+5+5+5
26 = 7+7+7+5
27 = 7+5+5+5+5
28 = 7+7+7+7
29 = 5 + 24
30 = 5+5+5+5+5+5
31 = 7 + 24
Inductive step: Assume every m with 24 ≤ m ≤ k (k ≥ 31) can be made.
Then k+1 − 5 ≥ 26 ≥ 24, so by the hypothesis k+1 − 5 is makeable; adding one 5‑cent stamp gives k+1.
Thus by strong induction, every n ≥ 24 is achievable with 7s and 5s.