1958 AMC 12 Problem 32

Attempt Problem 32 of the 1958 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1958 AMC 12 solutions, or check the answer key.

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32.

With $1000\$1000 a rancher is to buy steers at $25\$25 each and cows at $26\$26 each. If the number of steers ss and the number of cows cc are both positive integers, then:

this problem has no solution

there are two solutions with ss exceeding cc

there are two solutions with cc exceeding ss

there is one solution with ss exceeding cc

there is one solution with cc exceeding ss

Answer: E
Concepts:Diophantine Equationmodular arithmeticbounding to limit cases
Difficulty rating: 1630
Small Hint:

Write 25s+26c=100025s+26c=1000 and reduce it modulo 2525

Big Hint:

The congruence and positivity leave only one possible positive value of cc

Solution:

The purchase equation is 25s+26c=1000. 25s+26c=1000. Reducing modulo 2525 gives c0(mod25).c\equiv0\pmod{25}. Since cc is positive and 26c<1000,26c<1000, the only possibility is c=25.c=25. Then s=100026(25)25=14. s=\frac{1000-26(25)}{25}=14. There is one solution, and c>s.c>s.

Thus, the correct answer is E.

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