Page 293 - Ganit Kaushal

(b) Suppose we want to find (−5) + (+3).

Take 5 red coloured squares and 3 green coloured squares and –1 –1 –1 –1 –1
paste them on a white sheet of paper as shown in the adjoining +
figure. +1 +1 +1
We know that one green square and one red square will
neutralise each other. On counting the remaining ones after neutralising, we have 2 red squares
which represent (−2) as shown in the figure above.

Thus, (−5) + (+3) = −2

Activity 2

‘Measuring the temperature at various points of time in a day’

The objective of this activity is to help students understand the existence of integers 100 °C 100 °C
in their day to day life. This activity is to be done by the students at home by 90 90
measuring the atmospheric temperature at various points of time over a 24-hour 80 80
day and night period on a holiday (Saturday). For students living in hilly areas, 70 70
this temperature can be in negative integers also. 60 60
50 50
Teachers are advised to bring a laboratory thermometer to the class and measure 40 40
the temperature of hot and cold water in front of students so that they can learn to 30 30
measure the temperature. Point out to the children that there are markings on the 20 20
thermometer that are below 0°C. Have a discussion on what 0°C indicates, namely, 10 10
the freezing point of water. In the adjoining figure, two laboratory thermometers 0 0
are given showing the temperatures close to 20°C and 40°C. Ask each student –10 –10
to arrange such a thermometer, and measure the temperature of the atmosphere –20 –20
at various points of time at their home, and record it (the nearest integer) in the
following table.

Time Temperature

3:00 pm

5:00 pm

8:00 pm

10:00 pm

12:00 midnight

5:00 am

9:00 am

11:00 am

12:00 noon

291