12
12
They are: 3+3+3 = 9
Two-digit prime numbers whose digits add up to 10 are:193773
The number of digits increases - without limit.
804
It is 99,887,765
992
999,999 is 6 digits Adding 1 makes it 1,000,000 = a 7 digit number.
A quintillion is a number with 18 zeros (19 digits). A 20-digit number would be 10's of a quintillion (20 digits since we add one more digit to the left).
zero is used in the number system as a digit and a add on to other digits
17
44
537
That is correct. Considering the largest double digit whole number is 99. Unless of course, you mean adding the two digits of a double digit number alongside the two digits of another double digit number, then yes, you will have a 4 digit number. Depends how you interpret the question, and your creativity.