Subtracting Fractions – Step-by-Step
Subtracting fractions follows the same denominator rule as addition. Get a common denominator first, then subtract the numerators.
Case 1 - Like Fractions
7/9 - 4/9
(7-4)/9 = 3/9 = 1/3
Case 2 - Unlike Fractions
3/4 - 2/5
LCM(4,5) = 20. 3/4 = 15/20. 2/5 = 8/20. 15/20 - 8/20 = 7/20. Answer: 7/20.
5/6 - 3/8
LCM(6,8) = 24. 5/6 = 20/24. 3/8 = 9/24. 20/24 - 9/24 = 11/24. Answer: 11/24.
Case 3 - Mixed Numbers (No Borrowing)
4 and 3/4 minus 2 and 1/2
Wholes: 4-2=2. Fractions: 3/4 - 1/2. LCM=4: 3/4 - 2/4 = 1/4. Answer: 2 and 1/4.
Case 4 - Mixed Numbers (Borrowing Needed)
Convert to improper fractions to avoid errors.
5 and 1/3 minus 2 and 3/4
16/3 - 11/4. LCM=12: 64/12 - 33/12 = 31/12 = 2 and 7/12.
Subtracting from a Whole Number
5 - 3/4 = 4 and 1/4 (borrow 1 from 5 as 4/4; then 4/4 - 3/4 = 1/4)
Key Takeaways
- Find the LCD before subtracting unlike fractions.
- Subtract numerators; keep the denominator.
- Convert mixed numbers to improper fractions to avoid borrowing errors.
- Always simplify the answer.
Practice Questions
- 11/12 - 5/12
- 2/3 - 1/5
- 7/8 - 3/10
- 6 and 1/2 minus 2 and 3/4
- A plank is 3 and 1/3 m long. A carpenter cuts off 1 and 3/4 m. How much remains?