a and b are two positive integers such that the least prime factor of a is 3 and the least prime factor of b is 5. Then, the least prime factor of (a + b) is ______.

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a and b are two positive integers such that the least prime factor of a is 3 and the least prime factor of b is 5. Then, the least prime factor of (a + b) is 2. Explanation: Clearly, 2 is neither a factor of a nor that of b. ∴ a and b are both odd. Hence, (a + b) is even. ∴ Least prime factor of (a + b) is 2.

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