2014 AMC 10B Problem 12

Below is the professionally curated solution for Problem 12 of the 2014 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2014 AMC 10B solutions, or check the answer key.

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Concepts:factorprime factorization

Difficulty rating: 1280

12.

The largest divisor of 2,014,000,0002,014,000,000 is itself. What is its fifth-largest divisor?

125,875,000 125, 875, 000

201,400,000 201, 400, 000

251,750,000 251, 750, 000

402,800,000 402, 800, 000

503,500,000 503, 500, 000

Solution:

The fifth-largest divisor is 2,014,000,0002,014,000,000 divided by the fifth smallest divisor.

The prime factorization of 2,014,000,0002,014,000,000 is: 27561953.2^7\cdot 5^6 \cdot 19\cdot 53. This makes the first 55 smallest divisors 1,2,4,5,81,2,4,5,8 Therefore, the fifth smallest divisor is 8,8, and the fifth largest divisor must be: 20140000008=251750000.\dfrac{2014000000}8 =251750000.

Thus, the correct answer is C .

Problem 12 in Other Years