两个数都是7的倍数，两个数的和一定是7的倍数吗？

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Let's examine whether the sum of two multiples of 7 is always a multiple of 7. We can represent any multiple of 7 as 7 times some integer. For example, 14 equals 7 times 2, and 21 equals 7 times 3. Their sum is 35, which equals 7 times 5, so it's also a multiple of 7.