Problem Solving (PS) | Re: The least number which should be added to 28523 so that the sum is exa

The approach above is great (though not something you'll likely need to use on a GMAT question). Alternatively, if we know 28523 + k is divisible by both 5 and 8, then it must be divisible by 40, so it must have a units digit of zero. If 28523 + k has a units digit of zero, and k is positive, then k must have a units digit of 7, so only answer D can be right. We don't actually need to use the fact that the sum is divisible by 3 or 7.

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