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    EStimAting tHE Sum

                We can estimate the sum of two numbers by rounding off.
                Example 1. Find the actual as well as estimated sum of the following numbers:

                            a. 25 + 34                                   b.  48 + 73

                Solution. a. Actual Sum            Estimated Sum   b.  Actual Sum                    Estimated Sum
                                             round off                                       round off
                                     2 5                      3 0                    4 8                          5 0
                                 + 3 4       round off    + 3 0              +       7 3     round off     +      7 0
                                     5 9                      6 0                1 2 1                         1 2 0

                Example 2. A balloon-seller has 248 red balloons and 173 green balloons. Estimate

                the total number of balloons by rounding off to the nearest 10. Is the total number of
                balloons more than 400 or less than 400?
                Solution. Actual Sum                           Estimated Sum
                                               round off
                                2 4 8                               2 5 0
                             + 1 7 3           round off         + 1 7 0

                                4 2 1                               4 2 0
                Thus, the balloon-seller has more than 400 balloons.

                            Exercise 2E

                Find the actual sum first and then the estimated sum by rounding off to the nearest 10.
                Compare the sums. (one has been done for you.)

                                    round off                                               round off
                    1.       3 4                         3 0              2.        5 1
                         + 6 5      round off    +       7 0                     + 4 3      round off     +

                            9 9                      1 0 0
                             Actual sum < Estimated sum                        Actual sum ___ Estimated sum
                                    round off                                                round off
                    3.       4 6                                          4.        5 6

                         + 5 5       round off    +                              + 4 1      round off     +

                             Actual sum ___ Estimated sum                      Actual sum ___ Estimated sum
                                     round off                                               round off
                    5.       7 2                                          6.        5 9
                         + 1     1  round off     +                              + 3 5       round off    +

                             Actual sum ___ Estimated sum                      Actual sum ___ Estimated sum

                       48        Mathematics 3

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