TRICK #2: Adding Numbers that End with 9.
ADD: 39 + 25
Whenever you’re adding a number that ends in 9, first add 1 to the number in your head, so 39 + 1 = 40. Then subtract 1 from the other number, so 25 - 1 = 24. Finally, add the two “new” numbers, and you’ve got the answer.
40 + 24 = 64,
thus 39 + 25 = 64
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