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SAI INTERNATIONAL SCHOOL


                                                CBSE CURRICULUM


                                                       Class: VI

                                                 Lesson Note 10.2


                                             SUBJECT : Mathematics




               CH: 10 -The other side of zero


               SUBTOPIC:  Comparison, Addition, subtraction

                     Addition to keep track of movement

                   Start from the Food Court and press + 2 in the lift. Where will you reach? ____________

                     We can describe this using an expression:
                        Starting Floor + Movement = Target Floor.
                       The starting floor is + 1 (Food Court) and the number of button presses is + 2.
                       Therefore, you reach the target floor (+ 1) + (+ 2) = + 3
                     Combining button presses is also addition Gurmit was in the Toy Store and wanted to
                       go down two floors. But by mistake he pressed the ‘+’ button two times. He realised
                       his mistake and quickly pressed the ‘–’ button three times. How many floors below or
                       above the Toy Store will Gurmit reach? Gurmit will go one floor down. We can show
                       the movement resulting from combining button presses as an expression: (+2)  +  (–
                       3) =  –1.

                     Back to zero!
                       On the ground floor, Basant is in a great hurry and by mistake he presses +3. What
                       can he do to cancel it and stay on the ground floor? He can cancel it by pressing – 3.
                       That is, (+3) + (– 3) = 0. We call – 3 the inverse of +3. Similarly, the inverse of – 3 is +3.
                       If Basant now presses +4 and then presses – 4 in the lift, where will he reach? Here is
                       another way to think of the concept of inverse. If you are at Floor +4 and you press
                       its inverse – 4, then you are back to zero, the ground floor! If you are at Floor – 2 and
                       press its inverse +2, then you go to (– 2) + (+2) = 0, again the ground floor!

                     Subtraction to find which button to press.

                       In earlier classes, we understood the meaning of subtraction as ‘take away’. For
                       example, there are 10 books on the shelf. I take away 4 books. How many are left on
                       the shelf? We can express the answer using subtraction: 10 – 4 = 6 or ‘Ten take away
                       four is six.’
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