No.
No.
Well, 1 is equal to 1. 9 is equal to 9. So any number from 0 to 9. I do not think this is what is meant by the question. If you mean any number with more than one digit. There is no such number. Because 11 sums to 2. 19 sums to 10. 21 sums to 3. 29 sums to 11. 111 sums 3. 119 sums to 11. The sums do not grow as fast the increase of digits.
7X8=56
Neither; the sums are equal.
all the sums are 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,and 24
900
An infinite number.
A rhombus has four sides of equal length.
Yes
Emily worked out all the sums mentally.
What is the addend 600 rounded to the nearest hundred