2010 AMC 12B Problem 25
Attempt Problem 25 of the 2010 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 2010 AMC 12B solutions, or check the answer key.
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25.
For every integer let be the largest power of the largest prime that divides For example, What is the largest integer such that divides
Answer: D
Solution:
Since write the product as times a factor coprime to all four primes; then
Prime is a power of only when Since the values contribute
Prime when is the largest prime factor, i.e. with and every prime factor of at most excluding leaves values. The one with is adding So
Prime For with the numbers of allowable exponents are respectively. These terms alone contribute
Prime Write For the counts over total For the counts total each contributing two factors of Hence
Therefore
Thus, the correct answer is D.
Problem 25 in Other Years
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