Add long sums by making tens

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Learn it When you add a lot of numbers, look for pairs whose ones digits add up to 10, like 7 and 3, or 24 and 36. Each pair makes a whole ten, which is easy to add. Then add the tens together.

Example: 17 + 25 + 3 + 5

17 + 3 = 20 (7 and 3 make ten).
25 + 5 = 30 (5 and 5 make ten).
20 + 30 = 50.

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