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    regrouping tens

                    When we have more than 9 tens, we can regroup 10 tens into 1 hundred.

                              18 tens          1 hundred   8 tens

                    Example 3. Add 153 + 174.

                    Solution. Write the numbers in columns and add them.

                    Step 1. Add the ones.
                                                                                 H    T O
                                     3 + 4 = 7 ones

                                                                                 1   5    3

                                                                             +   1    7   4

                                                                                          7

                    Step 2. Add the tens and regroup.

                    5 + 7 = 12 tens = 1 hundred 2 tens
                    Write 2 in the tens place and carry over

                    1 to the hundreds column.

                                                             H    T O

                                                              1
                                                              1   5    3

                                                         +    1   7    4

                                                                  2    7

                    Step 3. Add the hundreds.                                            H    T O
                             1 + 1 + 1 = 3 hundreds                                      1
                    Write 3 in the hundreds place.                                       1   5    3

                    Therefore, 153 + 174 = 327.
                                                                                     +   1    7   4

                                                                                         3    2   7

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                                                                                                     Addition

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