Fractions & Decimals · Lesson 1 of 5

Simplify, Add, Subtract, Multiply, Divide, Mixed Numbers, and Converting to Decimals

Key rules and formulas, worked examples and 15 practice problems with step-by-step solutions.

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

  1. 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 ($$\frac{3}{5}$$)

  2. 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 ($$\frac{2}{3}$$)

  3. Problem 3

    Simplify $$\frac{84}{108}$$

    Show solution

    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

  1. 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 ($$\frac{5}{7}$$)

  2. 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 ($$\frac{7}{12}$$)

  3. 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

  1. 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 ($$\frac{2}{15}$$)

  2. 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 ($$\frac{1}{6}$$)

  3. 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

  1. 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 ($$\frac{3}{2}$$)

  2. 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 ($$\frac{5}{6}$$)

  3. 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

  1. 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).

  2. 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).

  3. 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).

Remember

Always simplify to the lowest terms. Find GCF of both numbers first.