Learn to subtract rational numbers including fractions and mixed numbers. Alberta Grade 9 curriculum.
Lesson 3.3 of Rational Numbers in Grade 9 Math — Alberta curriculum lessons.
To subtract rational numbers, we follow the same rules used for subtracting integers and fractions.
Integer Rules for Subtracting:• To subtract a positive integer, move to the left on the number line (decrease in value).• To subtract a negative integer, move to the right on the number line (increase in value).Remember: the first number is your starting position.
Let's try another:4 − (−3)Subtracting a negative is the same as adding the opposite.4 − (−3) = 4 + 3 = 7✅ Answer: 7So, when you subtract a negative number, the value increases.
When subtracting decimals, the rules are the same as with integers — but you must line up the decimal points carefully.• Subtracting a positive decimal decreases the total.• Subtracting a negative decimal increases the total.
When working with decimals, follow these simple steps:. 1. Check the signs.If both are positive, subtract normally. If one is negative, convert subtraction to addition (add the opposite).2. Rewrite the problem.Stack the numbers vertically.3. Line up the decimals!This keeps each place value (tenths, hundredths) in order.4. Subtract from right to left.Borrow where needed, just like whole numbers.
Don't subtract denominators!3/4 − 1/2 ≠ 2/2Always find a common denominator first, then subtract the numerators.
Fraction Rules for Subtracting:• To subtract fractions, we need a common denominator.• Once we have a common denominator, we subtract the numerators only (using integer rules).• The denominator stays the same.• Reduce to lowest terms if possible.
Don't subtract denominators!3/4 - 1/2 ≠ 2/2Always find a common denominator first, then subtract the numerators.
Subtracting rational numbers isn't just about math problems — it's used in everyday situations like finding temperature differences, calculating remaining materials, or determining distances.
In word problems, always:
Identify what's being subtracted. Write a subtraction sentence. Solve and explain what the result means.
2.4 − 1.7Step 1: Both numbers are positive: subtract normally.2.4 − 1.7 = 0.7✅ Answer: 0.7
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