Page 40 - Maths Skill - 3
P. 40

38                                                                                                  Maths


              Let’s Attempt


        Example 1:   Estimate the sum of 23 and 65 by rounding off the number to the nearest
                         tens.                                           Estimated sum              Actual sum

                                rounded to                                        T    O                  T    O
        Solution:        23     nearest tens       20                             2    0                  2     3

                                                                             +    7    0             +    6     5
                                rounded to                                        9    0                  8     8
                         65     nearest tens       70


                         Thus, the estimated sum is nearer to the actual sum but not correct.

        Example 2:   Estimate the sum of 133 and 274 by rounding off the numbers to the nearest

                         hundreds.                                      Estimated sum              Actual sum
                                    rounded to
        Solution:        133    nearest hundreds          100                 H T O                    H T O
                                                                              1    0   0               1
                                                                          +   3    0   0               1    3   3
                                    rounded to                                                     +   2    7   4
                         274    nearest hundreds          300                 4    0   0               4    0   7



                         Thus, the estimated sum is nearer to the actual sum but not correct.

        Example 3:   Estimate the sum of 759 and 367 by rounding off the numbers to the nearest
                         hundreds.                                      Estimated sum              Actual sum

                                    rounded to
        Solution:        759    nearest hundreds          800                 H T O                    H T O
                                                                                   0
                                                                              8
                                                                                       0
                                                                                                                9
                                                                                                            5
                                                                                                       7
                                                                          +   4    0   0           +   3    6   7
                                    rounded to                                12 0     0               11 2     6
                         367    nearest hundreds          400
                         Thus, the estimated sum is nearer to the actual sum but not correct.



                                                   Exercise 3.9



          1. Estimate the sum by rounding off the numbers to the nearest tens. Also, find the
              actual sum.
                (a)  65 + 24             (b)  46 + 33             (c)  55 + 31            (d) 73 + 18

          2. Estimate the sum by rounding off the numbers to the nearest hundreds. Also, find
              the actual sum.
                (a)  143 + 265           (b)  267 + 324           (c)  343 + 575          (d) 525 + 268
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