Numbers & Algebra
Operations with Integers, Rational Numbers and Exponents
Grade 7 · Grade 8 · Grade 9
- ✓By the end of this lesson students will be able to perform operations (addition, subtraction, multiplication, division) with integers.
- ✓By the end of this lesson students will be able to perform operations (addition, subtraction, multiplication, division) with rational numbers (fractions and decimals).
- ✓By the end of this lesson students will be able to apply the laws of exponents to simplify expressions.
- ✓By the end of this lesson students will be able to apply the correct order of operations (BODMAS) when solving problems involving integers, rational numbers, and exponents.
Key concepts
Integers are whole numbers and their opposites (negative numbers), including zero. They do not include fractions or decimals. Operations with integers follow specific rules for signs:\n- Addition: If signs are the same, add the absolute values and keep the sign. If signs are different, subtract the smaller absolute value from the larger absolute value and keep the sign of the number with the larger absolute value.\n- Subtraction: Change the subtraction to addition of the opposite number (e.g., a - b = a + (-b)).\n- Multiplication and Division: If signs are the same, the answer is positive. If signs are different, the answer is negative.
Rational numbers are numbers that can be expressed as a fraction p/q, where p and q are integers and q is not equal to zero. This includes integers, common fractions, mixed numbers, terminating decimals, and recurring decimals. Operations with rational numbers:\n- Addition and Subtraction of Fractions: Find a common denominator, then add or subtract the numerators.\n- Multiplication of Fractions: Multiply the numerators and multiply the denominators.\n- Division of Fractions: Multiply the first fraction by the reciprocal of the second fraction.\n- Operations with Decimals: Align decimal points for addition/subtraction. For multiplication, multiply as whole numbers then count decimal places. For division, make the divisor a whole number by shifting decimal points.
An exponent (or index) is a small number written above and to the right of a base number, indicating how many times the base number is multiplied by itself. For example, in a^n, 'a' is the base and 'n' is the exponent. The entire expression 'a^n' is called a power.\n\nLaws of Exponents:\n1. Product Rule: a^m × a^n = a^(m+n)\n2. Quotient Rule: a^m ÷ a^n = a^(m-n) (where a ≠ 0)\n3. Power Rule: (a^m)^n = a^(m×n)\n4. Zero Exponent: a^0 = 1 (where a ≠ 0)\n5. Negative Exponent: a^(-n) = 1/a^n (where a ≠ 0)\n6. Power of a Product: (ab)^n = a^n × b^n\n7. Power of a Quotient: (a/b)^n = a^n / b^n (where b ≠ 0)
When an expression involves multiple operations, we follow a specific order to ensure a consistent result. The acronym BODMAS helps us remember this order:\nB - Brackets (Parentheses)\nO - Orders (Exponents or Powers)\nD - Division and M - Multiplication (from left to right, whichever comes first)\nA - Addition and S - Subtraction (from left to right, whichever comes first)
Key facts to remember
- 1Integers include positive and negative whole numbers, and zero.
- 2Rational numbers can always be written as a fraction p/q, where q ≠ 0.
- 3BODMAS stands for Brackets, Orders (Exponents), Division/Multiplication (left to right), Addition/Subtraction (left to right).
- 4When multiplying or dividing integers, if the signs are the same, the answer is positive; if the signs are different, the answer is negative.
- 5Any non-zero number raised to the power of zero is equal to 1 (e.g., a^0 = 1).
- 6To divide by a fraction, you multiply by its reciprocal.
- 7A negative exponent indicates the reciprocal of the base raised to the positive exponent (e.g., a^(-n) = 1/a^n).
Worked examples
Example 1
Calculate: (-8) + 5 × (-3) - (-12)
Answer
-11
Remember to handle the signs carefully, especially with subtraction of negative numbers.
Example 2
Evaluate: (3/4 + 1/8) ÷ 0.25
Answer
7/2 or 3 1/2
It is often easier to work with fractions when mixing fractions and decimals in operations.
Example 3
Simplify: 2^3 + (5^2 - 10) × 3 / 3^1
Answer
23
Remember to evaluate exponents before multiplication or division, unless they are inside brackets.
Common mistakes
- ✗Incorrectly applying integer rules, especially with subtraction (e.g., -5 - 3 = -8, not -2).
- ✗Ignoring the order of operations (BODMAS), leading to incorrect results.
- ✗Making errors when adding or subtracting fractions by not finding a common denominator.
- ✗Incorrectly applying laws of exponents, such as (a+b)^n = a^n + b^n (this is incorrect).
- ✗Confusing -a^n with (-a)^n. For example, -2^2 = -4, but (-2)^2 = 4.
Exam tips
- ★Always show all your working steps clearly, as marks are often awarded for method.
- ★Double-check the signs of your numbers throughout the calculation, especially with integers.
- ★If a problem involves both fractions and decimals, consider converting all numbers to one form (usually fractions) to simplify calculations.
- ★Memorise the laws of exponents and practise applying them correctly to various problems.
- ★Practise using BODMAS regularly with mixed operations to build confidence and accuracy.
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