Use the doubles fact for addition.
4 + 5 = _____


Answer:

9

Step by Step Explanation:
  1. Here we need to calculate the sum of 4 and 5.
    Let us write 5 as 4 + 1 and use the doubles fact for addition.
    We get, 4 + 5 = 4 + 4 + 1
    = 8 + 1       [Using the doubles fact: 4 + 4 = 8 ]
    = 9
  2. We get, 4 + 5 = 9.

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