Page 10 - Start Up Mathematics_7

We know that on a number line, when we:

(i) add a positive integer or subtract a negative integer we move to the right.

(ii) subtract a positive integer or add a negative integer we move to the left.
Example 1: The following number line shows the temperature in degree Celsius (°C) at different
places on a particular day.

Srinagar Mysore Ooty Goa Delhi

–5 0 5 10 15 20 25
(a) Observe the number line and write the temperature of the places marked on it.
(b) What is the temperature difference between the hottest and the coldest places
shown above?
(c) Temperature of which place lies between Srinagar and Ooty?
(d) Can we say the difference in temperature of Mysore and Ooty is less than the
difference in temperature of Ooty and Goa?
Solution: (a) Temperature of the places marked on the number line are as follows:
(i) Srinagar = –3°C (ii) Mysore = 6°C (iii) Ooty = 11°C
(iv) Goa = 15°C (v) Delhi = 24°C
(b) Difference in temperature of two extreme climates = 24° – (–3°) = 27°C
(c) Temperature of Mysore lies between Srinagar and Ooty.
(d) Difference in temperature of Mysore and Ooty = 11° – 6° = 5°C

Difference in temperature of Ooty and Goa = 15° – 11° = 4°C
Thus, difference in temperature of Mysore and Ooty is not less than that of Ooty
and Goa.
Example 2: In Mussoorie, the temperature was 4°C on Monday and then it dropped by 6°C on
Tuesday. What was the temperature of Mussoorie on Tuesday? On Wednesday, it
rose by 4°C. What was the temperature on this day?
Solution: Temperature of Mussoorie on Monday = 4°C

Temperature on Tuesday = 4°C – 6°C = –2°C ( it dropped by 6°C)
Temperature on Wednesday = –2°C + 4°C = 2°C ( it rose by 4°C)

Example 3: A plane is flying at a height of 4,000 m above the sea level. At a particular point,
it is exactly above a submarine floating 1,000 m below the sea level. What is the
vertical distance between them?
Solution: The height of the plane = +4,000 m

The depth of the submarine = –1,000 m ( sea level is denoted by 0)
Vertical distance between the plane and submarine = 4,000 – (–1,000) = 5,000 m
Example 4: Mansi deposits ` 5,000 in her bank account and withdraws ` 3,500 from it, the next
day. If amount withdrawn from the account is represented by a negative integer, then
how will you represent the amount deposited? Find the balance in Mansi’s account
after the withdrawal.

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