Page 51 - ICSE Math 6

2. A bird is flying at 2,000 m above sea level. At a particular time it comes just above a submarine
which is 455 m below sea level. Find the distance between them when the bird is exactly above
the submarine.
3. Find the integer values represented by each of the following letters and then decode the given
message by replacing numbers with letters.
O: (+5) + (+3) V: (–2) + (7) M: (+8) – (–1)

S: (–8) + (+1) T: (–1) – (–5) G: (–6) + (+2)
Message: “I L85E 9A4HS”

Individual Activity

Objective: Use of number counters to understand addition of integers
Material required: Magenta and grey buttons, pencil, paper, tray
Demonstration: Use a grey button as a number counter representing +1 and a magenta
button as a number counter representing –1.
Case 1: Sum of two positive integers 3 and 2

Take 3 grey buttons to represent +3 and 2 grey buttons to represent +2.
Arrange the buttons in the tray and count the total number of
grey buttons.

There are 5 grey buttons, hence, 3 + 2 = 5.
Case 2: Sum of two negative integers –2 and –5

Take 2 magenta buttons to represent –2 and 5 magenta
buttons to represent –5.
Arrange them in the tray and count the total number of
magenta buttons.
There are 7 magenta buttons, hence, (–2) + (–5) = –7.
Case 3: Sum of a positive integer 4 and a negative integer –6

Take 4 grey buttons to represent +4 and 6 magenta buttons
to represent –6.

Place the buttons together in the tray and arrange them
pairwise taking one grey and one magenta button.
Each member of the pair cancels the other as the sum
become zero. The remaining 2 magenta buttons represents
the sum, i.e., +4 – 6 = –2.
Inference: Sum of two positive integers is positive, sum of two negative integers is negative
and sum of one positive and one negative integer takes the sign of the integer having the
greater absolute value.

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