+817 How many two-digit numbers have digits which add up to 7?
16
25
34
43
52
61
70
So, 7, right?
+1252 We have eight pairs.
{0, 7} {1, 6}{2, 5} {3, 4} {4, 3} {5, 2} {6, 1} {7, 0}
However, {0, 7} doesn't work because 7 is just a one digit number, so we have \(8-1=7\) total possibilities. You were right!
You are very welcome!
:P
