2016 AMC 12B Problem 24
Attempt Problem 24 of the 2016 AMC 12B 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 2016 AMC 12B solutions, or check the answer key.
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24.
There are exactly ordered quadruples such that and What is the smallest possible value of
Answer: D
Solution:
Writing each entry as times a reduced value, we need and For each prime dividing with maximum exponent the number of valid exponent quadruples is The total over all primes must equal Since equals and for and the exponents give one candidate factorization.
Every prime contributes exactly one factor of so exactly three primes divide Their odd factors must divide Checking the divisors gives with odd factors The choice leaves only for the product of the other two odd factors, but each is at least so this is impossible. Therefore the maximum exponents are exactly To minimize assign the largest exponent to the smallest prime: so
Thus, the correct answer is D.
Problem 24 in Other Years
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