2002 AMC 10A Problem 15

Below is the professionally curated solution for Problem 15 of the 2002 AMC 10A, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2002 AMC 10A solutions, or check the answer key.

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Concepts:primedigitsplace value

Difficulty rating: 1390

15.

The digits 1,1, 2,2, 3,3, 4,4, 5,5, 6,6, 7,7, and 99 are used to form four two-digit prime numbers, with each digit used exactly once. What is the sum of these four primes?

150150

160160

170170

180180

190190

Solution:

A two-digit prime cannot end in 2,2, 4,4, 5,5, or 6,6, so these four are the tens digits and 1,1, 3,3, 7,7, 99 are the units digits.

The sum is 10(2+4+5+6)+(1+3+7+9)=170+20=190.10(2+4+5+6)+(1+3+7+9)=170+20=190. One valid set is {23,47,59,61}.\{23,47,59,61\}.

Thus, the correct answer is E.

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