2016 AMC 10B Problems/Problem 6
Laura added two three-digit positive integers. All six digits in these numbers are different. Laura's sum is a three-digit number . What is the smallest possible value for the sum of the digits of ?
Let the two three-digit numbers she added be and with and . The hundreds digits of these numbers must be at least and , so and .
Say and ; then we just need with and having different digits which aren't or .There are many solutions, but and give which proves that is attainable.
For this problem, to find the -digit integer with the smallest sum of digits, one should make the units and tens digit add to . To do that, we need to make sure the digits are all distinct. For the units digit, we can have a variety of digits that work. works best for the top number which makes the bottom digit . The tens digits need to add to because of the that needs to be carried from the addition of the units digits. We see that and work the best as we can't use and . Finally, we use and for our hundreds place digits.
Adding the numbers and , we get which means our answer is .
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