SOLUTION: I am a 4 digit number greater than 9,000. My hundreds digit is twice my ones digit. My ones digit is greater than my tens digit. The sum of my digits is 20. What nu

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Suppose the number is 9abc

We know that a = 2c, c > b. Also, 9+a+b+c = 20, so a+b+c = 11. We can assume c = 0, c = 1, c = 2, etc. and find all the possible triples (a,b,c):

c = 0 --> a = 0, b = 11
c = 1 --> a = 2, b = 8
c = 2 --> a = 4, b = 5
c = 3 --> a = 6, b = 2

The first three cases don't work, because b > 9, or b is greater than c. The third case does work, so (a,b,c) = (6,2,3) and the number is 9623.