How many different positive integers exist between 10^6 and 10^7, the sum of whose digits is equal to 2? Choose the correct choice from the following answers: A) 6 B) 7 C) 5 D) 8 E) 18
So, the numbers should be from 1,000,000 to 10,000,000   The following two cases are possible for the sum of the digits to be 2:   1. Two 1's and the rest are 0's:   1,000,001   1,000,010   1,000,100   1,001,000   1,010,000   1,100,000   6 numbers.   2. One 2 and the rest are 0's:   2,000,000   1 number.   Total = 7 numbers.   Answer: 7.
<result>B</result>
How many different positive integers exist between 10^6 and 10^7, the sum of whose digits is equal to 2?