Integers are a collection of numerical values including positive numbers, zero and negative numbers.
Examples of integers include −100, −55, −20, −4, 0, 5, 10, 100, 1000, 10000, etc.
These integers can be visually represented on a number line, as shown below:
a. Closure Property: The closure property holds for addition, subtraction and multiplication with integers. In other words, when you perform these operations on two integers, the result is also an integer.
Examples: a) −5 + 4 = −1 (Integer)
b) 5 − 4 = 1 (Integer)
c) −5 × 4 = −20 (Integer)
b. Commutative Property: The commutative property applies to addition and multiplication in the set of integers. It means that the order of the integers does not affect the result.
For any two integers a and b,
a + b = b + a
Example: 4 + (−7) = (−7) + 4
Hence , 4 + (−7) = −3 and (−7) + 4 = −3.
a × b = b × a
Example: 4 × (−7) = (−7) × 4
Hence , 4 × (−7) = −28 and (−7) × 4 = −28.
c. Associative Property: The associative property holds for addition and multiplication in the set of integers. It means that the grouping of integers does not affect the result.
For any three integers a, b and c,
a + (b + c) = (a + b) + c
Example: 3 + (2 + (−4)) = (3 + 2) + (−4)
Hence, LHS = 3 + (2 + (−4))
= 3 + (2 − 4)
= 3 + (−2)
= 3 − 2
= 1
RHS = (3 + 2) + (−4)
= (5) + (−4)
= 5 −4
= 1
a × (b × c) = (a × b) × c
Example: 3 × (2 × (−4)) = (3 × 2) × (−4)
Hence, LHS = 3 × (2 × (−4)) = 3 × (−8) = −24
RHS = (3 × 2) × (−4) = (6) × (−4) = −24
d. Distributive Property: The distributive property applies to multiplication over addition and subtraction for integers. It allows you to distribute a factor across the sum or difference of integers.
For any three integers a, b and c,
a × (b + c) = a × b + a × c
Example: −4 × (3 + 2) = (−4 × 3) + (−4 × 2)
Hence, LHS = −4 × (3 + 2) = −4 × (5) = −20
RHS = (−4 × 3) + (−4 × 2) )
= (−12) + (−8)
= −12 − 8
= −20
a × (b − c) = a × b − a × c
Example: −4 × (3 − 2) = (−4 × 3) − (−4 × 2)
Hence, LHS = −4 × (3 − 2) = −4 × (1) = −4
RHS = (−4 × 3) − (−4 × 2)
= (−12) − (−8)
= −12 + 8
= −4
e. Identity Element: “0” is called the additive identity and “1” is called the multiplicative identity. In integers, when you add 0 to any integer or multiply any integer by 1, it remains unchanged.
For any integer a,
a + 0 = 0 + a = a
Examples: 7 + 0 = 0 + 7 = 7
a × 1 = 1 × a = a
Examples: 7 × 1 = 7 × 1 = 7
f. Multiplication by Zero: For any integer a, multiplying it by 0 results in 0 and the order of multiplication does not matter.
For any integer a, a × 0 = 0 × a = 0.
Example: 7 × 0 = 0 × 7 = 0
Example 1: Solve the given expression:
21 + (−13) × 17 − (−121)
a) −59
b) −79
c) 59
d) 79
Answer: b) −79
Explanation: 21 + (−13) × 17 − (−121)
= 21 + (−221) − (−121)
= 21 − 221 + 121
= 142 − 221
= −79
Example 2: In an olympiad exam, 4 marks are given for every correct answer and 1 mark is deducted for every incorrect answer. Xavier scored 27 marks though he got 11 correct answers. How many incorrect answers had he attempted?
a) 11
b) 13
c) 15
d) 17
Answer: d) 17
Explanation: Marks awarded for every correct answer = +4
Mark deducted for every incorrect answer = −1
Xavier scored 27 marks but he got 11 correct answers.
Marks scored by Xavier for correct answers = 4 × 11 = 44
But he scored 27 marks.
Marks deducted for incorrect answers = 44 − 27 = 17
Number of incorrect answers attempted = 17 ÷ 1 = 17
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