Sol. Ans.(d). From 700 to 1000 all the numbers apart from 1000 are of three digits. The sum of the digits of 1000 is not 10. So, we only have to check from 700 to 999.
Let the digits of the numbers a (hundreds place), b (tens place) and c (unit place).
a can have values 7, 8 and 9
b can have values from 0 to 9
c can have values from 0 to 9
Again a + b + c = 10
For (a, b, c), possible combinations are (7, 0, 3), (7, 1, 2), (7, 2, 1), (7, 3, 0), (8, 0, 2), (8, 1, 1), (8, 2, 0), (9, 0, 1) and (9, 1, 0).
So, total 9 numbers are possible.