2002 AMC 12A Problem 17

Below is the professionally curated solution for Problem 17 of the 2002 AMC 12A, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2002 AMC 12A solutions, or check the answer key.

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Concepts:primedigitsoptimization

Difficulty rating: 1800

17.

Several sets of prime numbers, such as {7,83,421,659},\{7, 83, 421, 659\}, use each of the nine nonzero digits exactly once. What is the smallest possible sum such a set of primes could have?

193193

207207

225225

252252

477477

Solution:

The even digits 4,6,84, 6, 8 cannot be the units digit of a multi-digit prime, so each must appear in a tens place or higher, contributing at least 40+60+80=180.40 + 60 + 80 = 180. The other six digits contribute at least 1+2+3+5+7+9=27,1 + 2 + 3 + 5 + 7 + 9 = 27, so the sum is at least 207.207.

This bound is achieved, for example by {2,3,5,41,67,89},\{2, 3, 5, 41, 67, 89\}, whose sum is 207.207.

Thus, the correct answer is B.

Problem 17 in Other Years