The question is a problem on counting properties in number theory.
Question 2
How many different positive integers exist between 106 and 107, the sum of whose digits is equal to 2?
A. 6
B. 7
C. 5
D. 8
E. 18
The correct choice is (B) and the correct answer is 7.
Explanatory Answer
Find the number of such integers existing for a lower power of 10 and extrapolate the results.
Between 10 and 100, that is 101 and 102, we have 2 numbers, 11 and 20.
Similarly, between 100 and 1000, that is 102 and 103, we have 3 numbers, 101, 110 and 200.
Therefore, between 106 and 107, one will have 7 integers whose sum will be equal to 2.
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This eBook covers all the topics in Number Theory and Inequalities related to GMAT. Explanation of topics provide in-depth knowledge of concepts such as LCM, HCF, remainder theorem in number theory and the rules governing inequalities. 
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