4-Digit Numbers Divisible by 7

Given the digits 1,3,6, and 9, find the probability that a four-digit number formed by using each of them only once is divisible by 7.
Source: NCTM Mathematics Teacher, February 2008

There are 4\times 3\times 2\times 1=24 possible four-digit numbers using 1,3,6,9 each only once
Numbers divisible by 7 are 3619,6139,6391,9163
Probability = 4/24=1/6.

Answer: 1/6


About mvtrinh

Retired high school math teacher.
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