Page 272 - Ganit Kaushal

Notice here that we are using the natural numbers with a ‘+’ sign in front for upward movement and a ‘–’ sign
in front for downward movement. A number with ‘+’ in front is called a positive number, and a number with
‘–’ in front is called a negative number.

Zero is neither a positive nor a negative number. So, we do not put a ‘+’ or a ‘–’ sign in front of it.

10.3 ADDITION AS BUTTON PRESSES

Now, start from the Sports Centre and press +3 in the lift. Building of Fun
Where do you reach?
Food Court +4
The Food Court on the fourth floor. Absolutely correct.

But how will you explain it? Art Gallery +3
Let us explain it using an expression: Cinema Hall +2

Starting Floor + Movement = Target Floor Sports Centre +1

Welcome Hall
The starting floor is +1 (Sports Centre), and the number of times the button (Ground Floor) 0
is pressed is +3, i.e., the movement is +3. Therefore, you reach the target
floor: (+1) + (+3) = +4 (Food Court). Books Library –1
Again, start from the Sports Centre and press the ‘–’ sign 3 times in the lift. Toy Store –2

Where do you reach?
The Toy Store on the −2 floor. Absolutely correct. So, you understand the above expression now
i.e., the starting floor is +1 (Sports Centre) and the button press is –3, i.e., the movement is –3. Therefore,
you reach the target floor: (+1) + (–3) = –2 (Toy Store).

So, we can say that:
Addition of positive button presses takes the lift up, and addition of
negative button presses takes the lift down.

Ex. Evaluate these expressions [you may think of them as (Starting Floor + Movement) by referring to the
Building of Fun]. (NCERT)

(a) (+1) + (+3) = ____ (b) (+4) + (−1) = ____ (c) (+4) + (–3) = ____ (d) (–1) + (+2) = ____
Sol. (a) (+1) + (+3) = +4 (already explained above).
(b) Here, the starting floor is +4 (Food Court); the movement is –1.

\ The lift will go down by one floor, so we will reach floor +3 (Art Gallery).
\ (+4) + (−1) = +3
(c) Here the starting floor is +4; the movement is –3.

\ The lift will go down by 3 floors, so we will reach floor +1 (Sports Centre).
\ (+4) + (−3) = +1
(d) Here the starting floor is –1 (Books Library); the movement is +2.
\ The lift will go up by 2 floors, so we will reach floor +1 (Sports Centre).

\ (– 1) + (+ 2) = +1

270 Mathematics-6