A rational number can be expressed as a repeating decimal if its denominator, when in simplest form, contains prime factors other than 2 or 5.
Let's analyze the given options:
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7/8: This has a denominator of 8, which is \(2^3\). It can be expressed as a terminating decimal.
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5/12: This has a denominator of 12, which is \(2^2 \times 3\). Since it includes a factor of 3, this can be expressed as a repeating decimal.
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17/25: This has a denominator of 25, which is \(5^2\). It can be expressed as a terminating decimal.
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31/40: This has a denominator of 40, which is \(2^3 \times 5\). It can also be expressed as a terminating decimal.
Based on this analysis, the only rational number from the options provided that can be expressed as a repeating decimal is 5/12.