how many different positive integers exist between 10 ^ 3 and 10 ^ 4 , the sum of whose digits is equal to 2 ?
"so , the numbers should be from 1,000 to 10,000 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 : 1,001 1,010 1,100 3 numbers . 2 . one 2 and the rest are 0 ' s : 2,000 1 number . total = 4 numbers . answer : d"
add(add(const_4, const_3), const_1)