What is 11/42 plus 9/21? (Answer: 29/42)

Exact Answer

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Problem: What is 11/42 plus 9/21?
Formula / Expression: 11/42 + 9/21
Final Answer: 29/42
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
Notice that 42 is an exact multiple of 21 (21 × 2 = 42). The Least Common Denominator (LCD) is simply 42, meaning we only need to scale one fraction.
Working: LCD(42, 21) = 42

Step 2: Convert to Equivalent Fractions with Common Denominator 42
Multiply the numerator and denominator of 11/42 by 1, and multiply the numerator and denominator of 9/21 by 2 so both fractions share the common base 42.
Working: 11 × 1/42 × 1 = 11/42 and 9 × 2/21 × 2 = 18/42

Step 3: Add the Numerators
Now add the numerators (11 + 18 = 29) and keep the common denominator 42 unchanged.
Working: 11 + 18/42 = 29/42

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 29 and 42 is 1, confirming that 29/42 cannot be reduced further—it is already in its simplest irreducible form.
Working: 29/42

Step 5: Decimal & Percentage Representation
Dividing the numerator 29 by denominator 42 produces a repeating decimal (approximately 0.690476, or 69.0476%).
Working: 29 ÷ 42 = 0.690476 (69.0476%)

Key Values:
- Simplified Fraction: 29/42
- Mixed Number Form: 29/42
- Decimal Value: 0.690476
- Percentage: 69.0476%

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Solved with FractionsCalc:
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11/42 + 9/21 = 29/42

Simplified Fraction

29/42

Mixed Number

Proper (29/42)

Decimal Value

0.690476

Percentage

69.0476%

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Step-by-Step Solution: 11/42 + 9/21

Step 1

Find the Least Common Denominator (LCD)

Notice that 42 is an exact multiple of 21 (21 × 2 = 42). The Least Common Denominator (LCD) is simply 42, meaning we only need to scale one fraction.

LCD(42, 21) = 42

Step 2

Convert to Equivalent Fractions with Common Denominator 42

Multiply the numerator and denominator of 11/42 by 1, and multiply the numerator and denominator of 9/21 by 2 so both fractions share the common base 42.

11 × 1/42 × 1 = 11/42 and 9 × 2/21 × 2 = 18/42

Step 3

Add the Numerators

Now add the numerators (11 + 18 = 29) and keep the common denominator 42 unchanged.

11 + 18/42 = 29/42

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 29 and 42 is 1, confirming that 29/42 cannot be reduced further—it is already in its simplest irreducible form.

29/42

Step 5

Decimal & Percentage Representation

Dividing the numerator 29 by denominator 42 produces a repeating decimal (approximately 0.690476, or 69.0476%).

29 ÷ 42 = 0.690476 (69.0476%)

Visual Representation

The diagram below illustrates 11/42 plus 9/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`29/42`
Mixed Number Form	`29/42`
Decimal Form	`0.690476`
Percentage	`69.0476%`

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Frequently Asked Questions

What is 11/42 plus 9/21 as a fraction?

11/42 + 9/21 in simplest fraction form is 29/42.

What is 11/42 plus 9/21 as a decimal?

11/42 + 9/21 converted to a decimal is 0.690476.

What is 11/42 plus 9/21 as a percentage?

11/42 + 9/21 expressed as a percentage is 69.0476%.

Does 11/42 plus 9/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.690476...) because the denominator contains prime factors other than 2 and 5.