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The question is a problem on counting properties in number theory.

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.

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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