How many different positive integers exist between 10^7 and 10^8, the sum of whose digits is equal to 2? Answers.
A) 6	B) 7	C) 5	D) 8	E) 18
So, the numbers should be from 10,000,000 to 100,000,000   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:   10,000,001   10,000,010   10,000,100   10,001,000   10,010,000   10,100,000   11,000,000   7 numbers.   2. One 2 and the rest are 0's:   20,000,000   1 number.   Total = 8 numbers.   Answer: 8
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How many different positive integers exist between 10^7 and 10^8, the sum of whose digits is equal to 2?