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Operations with Integers - A Quick Recap of Integers

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Integers are a set of numbers consisting of whole numbers and their negatives: Z={…,−3,−2,−1,0,1,2,3,… }\mathbb{Z} = \{ \dots, -3, -2, -1, 0, 1, 2, 3, \dots \}.

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On a number line, adding a positive integer moves the point to the right, while adding a negative integer moves it to the left.

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The absolute value of an integer aa, denoted by ∣a∣|a|, is its numerical value regardless of its sign. For example, ∣−5∣=5|-5| = 5 and ∣5∣=5|5| = 5.

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When adding two integers with the same sign, add their absolute values and keep the common sign. For different signs, subtract the smaller absolute value from the larger one and use the sign of the integer with the larger absolute value.

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The additive inverse of any integer aa is −a-a, such that a+(−a)=0a + (-a) = 0.

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Rules for Multiplication and Division: (+)×(+)=(+)(+) \times (+) = (+), (−)×(−)=(+)(-) \times (-) = (+), (+)×(−)=(−)(+) \times (-) = (-), and (−)×(+)=(−)(-) \times (+) = (-). Same rules apply for division.

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Properties include the Commutative Property (a+b=b+aa + b = b + a), Associative Property (a+(b+c)=(a+b)+ca + (b + c) = (a + b) + c), and the Distributive Property of multiplication over addition (a×(b+c)=a×b+a×ca \times (b + c) = a \times b + a \times c).

📐Formulae

a−(−b)=a+ba - (-b) = a + b

a+(−b)=a−ba + (-b) = a - b

(−a)×(−b)=ab(-a) \times (-b) = ab

(−a)×(b)=−(ab)(-a) \times (b) = -(ab)

a÷(−b)=−aba \div (-b) = -\frac{a}{b}

(−a)÷(−b)=ab(-a) \div (-b) = \frac{a}{b}

💡Examples

Problem 1:

Evaluate the following addition: (−15)+(−28)(-15) + (-28)

Solution:

(−15)+(−28)=−43(-15) + (-28) = -43

Explanation:

Since both integers have the same sign (negative), we add their absolute values: 15+28=4315 + 28 = 43. We then apply the common negative sign to the result.

Problem 2:

Subtract −45-45 from 8080.

Solution:

80−(−45)125\begin{array}{r} 80 \\ -(-45) \\ \hline 125 \end{array}

Explanation:

Subtracting a negative number is the same as adding its positive counterpart: 80−(−45)=80+45=12580 - (-45) = 80 + 45 = 125.

Problem 3:

Find the product: (−5)×(−2)×(−3)(-5) \times (-2) \times (-3)

Solution:

(−5)×(−2)×(−3)=10×(−3)=−30(-5) \times (-2) \times (-3) = 10 \times (-3) = -30

Explanation:

First, multiply the first two integers: (−5)×(−2)=10(-5) \times (-2) = 10 (product of two negatives is positive). Then, multiply by the third integer: 10×(−3)=−3010 \times (-3) = -30 (product of positive and negative is negative).

Problem 4:

Simplify using the distributive property: 25×(−98)25 \times (-98)

Solution:

25×[(−100)+2]=(25×−100)+(25×2)=−2500+50=−245025 \times [(-100) + 2] = (25 \times -100) + (25 \times 2) = -2500 + 50 = -2450

Explanation:

We express −98-98 as (−100+2)(-100 + 2) to make the calculation easier using the formula a×(b+c)=ab+aca \times (b + c) = ab + ac.