2001 AMC 8 Problem 25
Below is the professionally curated solution for Problem 25 of the 2001 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2001 AMC 8 solutions, or check the answer key.
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Difficulty rating: 1680
25.
There are four-digit whole numbers that use each of the four digits and exactly once. Only one of these four-digit numbers is a multiple of another one. Which of the following is it?
Solution:
A number in the , , or range cannot be multiplied by or more and remain one of the given four-digit permutations. So the smaller number must start with , and the larger number must be either double or triple it.
For doubles, only answer choices ending in can work. But and , neither of which uses exactly the digits .
For triples, the possible answer choices are those divisible by : . Dividing gives , and only uses exactly the required digits.
Therefore is the unique listed multiple.
Thus, D is the correct answer.
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