Fractions and Decimals Operations
Core Formulas and Rules
1. Simplify Fractions: $$\frac{(a \div n)}{(b \div n)}$$
Divide numerator and denominator by their Greatest Common Factor (GCF).
Example
Simplify $$\frac{12}{18}$$
Show solution
Step 1: Find the Greatest Common Factor (GCF) of 12 and 18:
- Factors of 12: 1, 2, 3, 4, 6, 12
- Factors of 18: 1, 2, 3, 6, 9, 18
=> GCF(12, 18) = 6.
Step 2: Divide both numerator and denominator by 6:
- Numerator: $$12 \div 6 = 2$$
- Denominator: $$18 \div 6 = 3$$
Result: $$\frac{2}{3}$$
Practice problems
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Problem 1
Simplify $$\frac{6}{10}$$
Show solution
Answer: $$\frac{3}{5}$$
Step 1: Find the GCF of 6 and 10:
- Factors of 6: {1, 2, 3, 6}
- Factors of 10: {1, 2, 5, 10}
=> GCF(6, 10) = 2.
Step 2: Divide numerator and denominator by 2:
- New numerator = $$6 \div 2 = 3$$
- New denominator $$= 10 \div 2 = 5$$
=> Correct Answer: A ($$\frac{3}{5}$$)
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Problem 2
Simplify $$\frac{24}{36}$$
Show solution
Answer: $$\frac{2}{3}$$
Step 1: Find GCF using prime factorization:
- $$24 = 2^3 \times 3$$
- $$36 = 2^2 \times 3^2$$
=> GCF(24, 36) $$= 2^2 \times 3 = 12$$.
Step 2: Divide numerator and denominator by 12:
- Numerator: $$24 \div 12 = 2$$
- Denominator: $$36 \div 12 = 3$$
=> Correct Answer: A ($$\frac{2}{3}$$)
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Problem 3
Simplify $$\frac{84}{108}$$
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Answer: $$\frac{7}{9}$$
Step 1: Find GCF(84, 108) using the Euclidean Algorithm:
- $$108 = 84 \times 1 + 24$$
- $$84 = 24 \times 3 + 12$$
- $$24 = 12 \times 2 + 0$$ => GCF is 12.
Step 2: Simplify the fraction:
- Numerator: $$84 \div 12 = 7$$
- Denominator: $$108 \div 12 = 9$$
=> Correct Answer: B ($$\frac{7}{9}$$)
2. Add / Subtract: a/c ± $$\frac{b}{c} = \frac{(a \pm b)}{c}$$
Find a Common Denominator (LCD). Adjust numerators, then add or subtract.
Example
Calculate $$\frac{1}{4} + \frac{1}{6}$$
Show solution
Step 1: Find the Least Common Denominator (LCD) of 4 and 6:
- Multiples of 4: 4, 8, 12, 16...
- Multiples of 6: 6, 12, 18...
=> LCD(4, 6) = 12.
Step 2: Convert both fractions to equivalent fractions with denominator 12:
- $$\frac{1}{4} = \frac{(1 \times 3)}{(4 \times 3)} = \frac{3}{12}$$
- $$\frac{1}{6} = \frac{(1 \times 2)}{(6 \times 2)} = \frac{2}{12}$$
Step 3: Add numerators, keep denominator:
- $$\frac{3}{12} + \frac{2}{12} = \frac{(3+2)}{12} = \frac{5}{12}$$
Practice problems
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Problem 4
Calculate $$\frac{2}{7} + \frac{3}{7}$$
Show solution
Answer: $$\frac{5}{7}$$
Step 1: Observe both fractions already share the same denominator (7).
Step 2: Add numerators and keep the common denominator:
- New numerator = $$2 + 3 = 5$$
- Denominator = 7
=> Resulting fraction: $$\frac{5}{7}$$.
=> Correct Answer: B ($$\frac{5}{7}$$)
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Problem 5
Calculate $$\frac{3}{4} - \frac{1}{6}$$
Show solution
Answer: $$\frac{7}{12}$$
Step 1: Find the Least Common Denominator: LCD(4, 6) = 12.
Step 2: Convert to equivalent fractions:
- For $$\frac{3}{4}$$: multiplier $$= 12 \div 4 = 3 \Rightarrow \frac{(3 \times 3)}{(4 \times 3)} = \frac{9}{12}$$
- For $$\frac{1}{6}$$: multiplier $$= 12 \div 6 = 2 \Rightarrow \frac{(1 \times 2)}{(6 \times 2)} = \frac{2}{12}$$
Step 3: Subtract numerators:
- $$\frac{9}{12} - \frac{2}{12} = \frac{(9 - 2)}{12} = \frac{7}{12}$$.
=> Correct Answer: A ($$\frac{7}{12}$$)
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Problem 6
Calculate $$\frac{5}{8} + \frac{1}{6} - \frac{1}{4}$$
Show solution
Answer: $$\frac{13}{24}$$
Step 1: Find LCD of all 3 denominators (8, 6, 4):
- $$8 = 2^3$$, $$6 = 2 \times 3$$, $$4 = 2^2 \Rightarrow \text{LCD}(8, 6, 4) = 24$$.
Step 2: Convert all fractions to denominator 24:
- $$\frac{5}{8} = \frac{(5 \times 3)}{24} = \frac{15}{24}$$
- $$\frac{1}{6} = \frac{(1 \times 4)}{24} = \frac{4}{24}$$
- $$\frac{1}{4} = \frac{(1 \times 6)}{24} = \frac{6}{24}$$
Step 3: Combine numerators from left to right:
- $$\frac{(15 + 4 - 6)}{24} = \frac{13}{24}$$.
=> Correct Answer: A ($$\frac{13}{24}$$)
3. Multiply: $$\frac{a}{b} \times \frac{c}{d} = \frac{(a \times c)}{(b \times d)}$$
Multiply numerators together and denominators together. Simplify if needed.
Example
Calculate $$\frac{2}{3} \times \frac{3}{5}$$
Show solution
Step 1: Multiply numerators together and denominators together:
- Numerator = $$2 \times 3 = 6$$
- Denominator $$= 3 \times 5 = 15$$
=> Intermediate fraction: $$\frac{6}{15}$$
Step 2: Simplify by dividing by GCF = 3:
- $$6 \div 3 = 2$$
- $$15 \div 3 = 5$$
=> Simplified fraction: $$\frac{2}{5}$$.
(Alternative: Cross-cancel 3 before multiplying: $$(\frac{2}{3}) \times (\frac{3}{5}) = \frac{2}{5}$$).
Practice problems
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Problem 7
Calculate $$\frac{1}{3} \times \frac{2}{5}$$
Show solution
Answer: $$\frac{2}{15}$$
Step 1: Multiply the numerators:
- New numerator = $$1 \times 2 = 2$$
Step 2: Multiply the denominators:
- New denominator $$= 3 \times 5 = 15$$
Step 3: Check simplification: GCF(2, 15) = 1, so $$\frac{2}{15}$$ is already simplified.
=> Correct Answer: A ($$\frac{2}{15}$$)
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Problem 8
Calculate $$\frac{4}{9} \times \frac{3}{8}$$
Show solution
Answer: $$\frac{1}{6}$$
Method 1 (Multiply then simplify):
- Numerator: $$4 \times 3 = 12$$
- Denominator: $$9 \times 8 = 72$$
- Simplify $$\frac{12}{72}$$ by dividing by $$12 \Rightarrow \frac{1}{6}$$.
Method 2 (Cross-cancel first):
- Cancel 4 and 8 (divide by 4): 4 becomes 1, 8 becomes 2
- Cancel 3 and 9 (divide by 3): 3 becomes 1, 9 becomes 3
- Result: $$(\frac{1}{3}) \times (\frac{1}{2}) = \frac{1}{6}$$.
=> Correct Answer: A ($$\frac{1}{6}$$)
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Problem 9
Calculate $$\frac{5}{12} \times \frac{8}{15} \times \frac{9}{10}$$
Show solution
Answer: $$\frac{1}{5}$$
Step 1: Express as a single large fraction:
- Numerator = $$5 \times 8 \times 9$$
- Denominator $$= 12 \times 15 \times 10$$
Step 2: Cross-cancel factors:
- Cancel 5 with 15 (divide by 5): 5 -> 1, 15 -> 3
- Cancel 9 with 3 (divide by 3): 9 -> 3
- Cancel 3 with 12 (divide by 3): 12 -> 4
- Cancel 8 with 4 (divide by 4): 8 -> 2
- Cancel 2 with 10 (divide by 2): 10 -> 5
Step 3: Multiply remaining terms: $$\frac{1}{5}$$.
=> Correct Answer: B ($$\frac{1}{5}$$)
4. Divide: $$\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c}$$
Multiply the first fraction by the reciprocal (flipped version) of the second fraction.
Example
Calculate $$\frac{3}{4} \div \frac{2}{5}$$
Show solution
Step 1: Keep the first fraction $$(\frac{3}{4})$$.
Step 2: Change division $$( \div )$$ to multiplication $$( \times )$$.
Step 3: Flip the second fraction ($$\frac{2}{5}$$ becomes $$\frac{5}{2}$$).
Step 4: Multiply fractions:
- $$(\frac{3}{4}) \times (\frac{5}{2}) = \frac{(3 \times 5)}{(4 \times 2)} = \frac{15}{8}$$
Practice problems
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Problem 10
Calculate $$\frac{1}{2} \div \frac{1}{3}$$
Show solution
Answer: $$\frac{3}{2}$$
Step 1: Keep the first fraction: $$\frac{1}{2}$$.
Step 2: Change ÷ to × and flip $$\frac{1}{3}$$ to $$\frac{3}{1}$$:
- $$\frac{1}{2} \div \frac{1}{3} = \frac{1}{2} \times \frac{3}{1}$$
Step 3: Multiply numerators and denominators:
- $$\frac{(1 \times 3)}{(2 \times 1)} = \frac{3}{2}$$.
=> Correct Answer: A ($$\frac{3}{2}$$)
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Problem 11
Calculate $$\frac{5}{8} \div \frac{3}{4}$$
Show solution
Answer: $$\frac{5}{6}$$
Step 1: Apply Keep-Change-Flip:
- $$\frac{5}{8} \div \frac{3}{4} = \frac{5}{8} \times \frac{4}{3}$$
Step 2: Cross-cancel before multiplying:
- Cancel 4 and 8 (divide by 4): 4 becomes 1, 8 becomes 2
- Calculation becomes: $$(\frac{5}{2}) \times (\frac{1}{3})$$
Step 3: Multiply results:
- $$\frac{(5 \times 1)}{(2 \times 3)} = \frac{5}{6}$$.
=> Correct Answer: A ($$\frac{5}{6}$$)
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Problem 12
Calculate $$(\frac{2}{3} \div \frac{4}{5}) \div \frac{5}{6}$$
Show solution
Answer: 1
Step 1: Calculate inside parentheses first:
- $$\frac{2}{3} \div \frac{4}{5} = \frac{2}{3} \times \frac{5}{4} = \frac{10}{12}$$
- Simplify $$\frac{10}{12}$$ by dividing by 2: $$\frac{5}{6}$$.
Step 2: Calculate outer expression:
- Divide result $$(\frac{5}{6})$$ by $$\frac{5}{6}$$:
- $$\frac{5}{6} \div \frac{5}{6} = \frac{5}{6} \times \frac{6}{5} = \frac{30}{30} = 1$$.
=> Correct Answer: B (1).
5. To Decimal: $$a \div b$$
Divide the numerator (a) by the denominator (b).
Example
Convert $$\frac{3}{4}$$ to decimal.
Show solution
Perform long division of numerator by denominator $$(3 \div 4)$$:
- 3 is less than 4, write 0 and a decimal point => 0.
- Add 0 after 3 to make 30.
- $$30 \div 4 = 7 \; (\mathrm{remainder} \; 2)$$.
- Add 0 to remainder 2 to make 20.
- $$20 \div 4 = 5 \; (\mathrm{remainder} \; 0)$$.
=> Result: 0.75.
Practice problems
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Problem 13
Convert $$\frac{1}{2}$$ to decimal.
Show solution
Answer: 0.5
Perform long division $$1 \div 2$$:
- $$1 \div 2 = 0$$ with a decimal point (0.)
- Add zero to 1 to make 10
- $$10 \div 2 = 5 \; (\mathrm{remainder} \; 0)$$
=> Result: 0.5.
=> Correct Answer: A (0.5).
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Problem 14
Convert $$\frac{7}{8}$$ to decimal.
Show solution
Answer: 0.875
Step-by-step long division of 7 by 8:
- $$7 \div 8 = 0$$., add zero to make 70.
- $$70 \div 8 = 8 (8 \times 8 = 64)$$, remainder = 6.
- Add zero -> 60. $$60 \div 8 = 7 (8 \times 7 = 56)$$, remainder = 4.
- Add zero -> 40. $$40 \div 8 = 5 (8 \times 5 = 40)$$, remainder = 0.
=> Combine digits: 0.875.
=> Correct Answer: A (0.875).
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Problem 15
Convert $$\frac{13}{16}$$ to decimal.
Show solution
Answer: 0.8125
Step-by-step long division of 13 by 16:
- $$13 \div 16 = 0$$., add zero -> 130.
- $$130 \div 16 = 8 (16 \times 8 = 128)$$, remainder = 2.
- Add zero -> 20. $$20 \div 16 = 1 (16 \times 1 = 16)$$, remainder = 4.
- Add zero -> 40. $$40 \div 16 = 2 (16 \times 2 = 32)$$, remainder = 8.
- Add zero -> 80. $$80 \div 16 = 5 (16 \times 5 = 80)$$, remainder = 0.
=> Exact decimal: 0.8125.
=> Correct Answer: B (0.8125).
Always simplify to the lowest terms. Find GCF of both numbers first.