Class 9 Maths The World of Numbers Exercise Set 3.2 Solutions | Ganita Manjari

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Class 9 Maths – The World of Numbers

Exercise Set 3.2 Solutions | Ganita Manjari

Question 1

The temperature in the high-altitude desert of Ladakh is recorded as 4°C at noon. By midnight, it drops by 15°C. What is the midnight temperature?

Solution

Temperature at noon = 4°C

Drop in temperature = 15°C

Therefore,

4 − 15 = −11

Hence, the midnight temperature is −11°C.

Question 2

A spice trader takes a loan (debt) of ₹850. The next day, he makes a profit of ₹1200. The following week, he incurs a loss of ₹450. Write this sequence as an equation using integers and calculate his final financial standing.

Solution

Loan of ₹850 represents debt:

−850

Profit of ₹1200:

+1200

Loss of ₹450:

−450

Required equation:

−850 + 1200 − 450

First add:

−850 + 1200 = 350

Now subtract:

350 − 450 = −100

Therefore, the trader’s final financial standing is −₹100.

This means he is still in debt of ₹100.

Question 3

Calculate the following using Brahmagupta’s laws:

(i) (−12) × 5

Solution

A negative number multiplied by a positive number gives a negative number.

(−12) × 5 = −60

(ii) (−8) × (−7)

Solution

A negative number multiplied by another negative number gives a positive number.

(−8) × (−7) = 56

(iii) 0 − (−14)

Solution

Subtracting a negative number is the same as adding the positive number.

0 − (−14)

= 0 + 14

= 14

(iv) (−20) ÷ 4

Solution

A negative number divided by a positive number gives a negative number.

(−20) ÷ 4 = −5

Question 4

Explain, using a real-world example of debt, why subtracting a negative number is the same as adding a positive number.

Solution

Suppose a person has ₹10 and a debt of ₹5.

Removing the debt means subtracting a negative quantity.

10 − (−5)

= 10 + 5

= 15

Hence, subtracting a negative number is the same as adding a positive number.

Students should also practice Exercise Set 1.3 and other important questions from the chapter “The World of Numbers” to strengthen their understanding of integers and number operations. You can also explore chapter-wise solutions, topper practice papers, worksheets, and periodic tests of Class 9 Maths available on our website.