Students can Download Maths Chapter 1 Number System Ex 1.3 Questions and Answers, Notes Pdf, Samacheer Kalvi 7th Maths Book Solutions Guide Pdf helps you to revise the complete Tamilnadu State Board New Syllabus and score more marks in your examinations.

## Tamilnadu Samacheer Kalvi 7th Maths Solutions Term 1 Chapter 1 Number System Ex 1.3

Question 1.

Fill in the blanks.

(i) -80 × ____ = -80

(ii) (-10) × ____ = 20

(iii) 100 × ___ = -500

(iv) ____ × (-9) = -45

(v) ___ × 75 = 0

Solution:

(i) 1

(ii) -2

(iii) -5

(iv) 5

(v) 0

Question 2.

Say True or False:

(i) (-15) × 5 = 75

(ii) (-100) × 0 × 20 = 0

(iii) 8 × (-4) = 32

Solution:

(i) False

(ii) True

(iii) False

Question 3.

What will be the sign of the product of the following:

(i) 16 times of negative integers.

(ii) 29 times of negative integers.

Solution:

(i) 16 is an even interger.

If negative integers are multiplied even number of times, the product is a positive integer.

∴ 16 times a negative integer is a positive integer.

(ii) 29 times negative integer.

If negative integers are multiplied odd number of times, the product is a negative integer. 29 is odd.

∴ 29 times negative integers is a negative integer.

Question 4.

Find the product of

(i) (-35) × 22

(ii) (-10) × 12 × (-9)

(iii) (-9) × (-8) × (-7) × (-6)

(iv) (-25) × 0 × 45 × 90

(v) (-2) × (+50) × (-25) × 4

Solution:

(i) 35 × 22 = -770

(ii) (-10) × 12 × (-9) = (-120) × (-9) = +1080

(iii) (-9) × (-8) × (-7) × (-6) = (+72) × (-7) × (-6) = (-504) × (-6) = +3024

(iv) (-25) × 0 × 45 × 90 = 0 × 45 × 90 = 0 × 90 = 0

(v) (-2) × (+50) × (-25) × 4 = (-100) × -25 × 4 = 2500 × 4 = 10,000

Question 5.

Check the following for equality and if they are equal, mention the property.

(i) (8 – 13) × 7 and 8 – (13 × 7)

Solution:

Consider (8 – 13) × 7 = (-5) × 7 = -35

Now 8 – (13 × 7) = 8 – 91 = -83

∴ (8 – 13) × 7 ≠ 8 – (13 × 7)

(ii) [(-6) – (+8)] × (-4) and (-6) – [8 × (-4)]

Solution:

[(-6) – (+8)] × (-4) = [(-6) + (-8)] × (-4) = (-14) × (-4) = +56

Now (-6) – [8 × (-4)] = (-6) – (-32)

= (-6) + (+32) = +26

∴ [(-6) – (+8)] × (-4) ≠ (-6) – [8 × (-4)]

(iii) 3 × [(-4) + (-10)] and [3 × (-4) + 3 × (-10)]

Solution:

Consider 3 × [(-4) + (-10)] = 3 × -14 = -42

Now [3 × (-4) + 3 × (-10)] = (-12) + (-30) = -42

Here 3 × [(-4) + (-10)] = [3 × (-4) + 3 × (-10)]

It is the distributive property of multiplication over addition.

Question 6.

During summer, the level of the water in a pond decreases by 2 inches every week due to evaporation. What is the change in the level of the water over a period of 6 weeks?

Solution:

Level of water decreases a week = 2 inches.

Level of water decreases in 6 weeks = 6 × 2 = 12 inches

Question 7.

Find all possible pairs of integers that give a product of -50.

Solution:

Factor of 50 are 1, 2, 5, 10, 25, 50.

Possible pairs of integers that gives product -50:

(-1 × 50), (1 × (-50)), (-2 × 25), (2 × (-25)), (-5 × 10), (5 × (-10))

Objective Type Questions

Question 8.

Which of the following expressions is equal to -30.

(i) -20 – (-5 × 2)

(ii) (6 × 10) – (6× 5)

(iii) (2 × 5)+ (4 × 5)

(iv) (-6) × (+5)

Solution:

(iv) (-6) × (+5)

Hint:

(i) -20 + (10) = -10

(ii) 60 – 30 = 30

(iii) 10 + 20 = 30

(iv) (-6) × (+5) = – 30

Question 9.

Which property is illustrated by the equation: (5 × 2) + (5 × 5) = 5 × (2 + 5)

(i) commutative

(ii) closure

(iii) distributive

(iv) associative

Solution:

(iii) distributive

Question 10.

11 × (-1) = _____

(i) -1

(ii) 0

(iii) +1

(iv) -11

Solution:

(iv) -11

Question 11.

(-12) × (-9) =

(i) 108

(ii) -108

(iii) +1

(iv) -1

Solution:

(i) 108