Add:
1
+9


Answer:

10

Step by Step Explanation:
  1. We know that to add 9, we need to take the first addend and count up to 9 digits to obtain the result.
  2. To add 9 to 1, let us begin counting from 1.
    1 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 110
  3. We see that by adding 9 to 1 we get 10.
    So,
    1
    +9
    10

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