What is 12/55 plus 9/21? (Answer: 249/385)

Exact Answer

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Problem: What is 12/55 plus 9/21?
Formula / Expression: 12/55 + 9/21
Final Answer: 249/385
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 55 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 55 × 21 = 1155.
Working: LCD(55, 21) = 1155

Step 2: Convert to Equivalent Fractions with Common Denominator 1155
Multiply the numerator and denominator of 12/55 by 21, and multiply the numerator and denominator of 9/21 by 55 so both fractions share the common base 1155.
Working: 12 × 21/55 × 21 = 252/1155 and 9 × 55/21 × 55 = 495/1155

Step 3: Add the Numerators
Now add the numerators (252 + 495 = 747) and keep the common denominator 1155 unchanged.
Working: 252 + 495/1155 = 747/1155

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 747 and 1155, which is 3. Divide both the numerator and denominator by 3.
Working: 747 ÷ 3/1155 ÷ 3 = 249/385

Step 5: Decimal & Percentage Representation
Dividing the numerator 249 by denominator 385 produces a repeating decimal (approximately 0.646753, or 64.6753%).
Working: 249 ÷ 385 = 0.646753 (64.6753%)

Key Values:
- Simplified Fraction: 249/385
- Mixed Number Form: 249/385
- Decimal Value: 0.646753
- Percentage: 64.6753%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-12-55-plus-9-21/
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12/55 + 9/21 = 249/385

Simplified Fraction

249/385

Mixed Number

Proper (249/385)

Decimal Value

0.646753

Percentage

64.6753%

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Step-by-Step Solution: 12/55 + 9/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 55 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 55 × 21 = 1155.

LCD(55, 21) = 1155

Step 2

Convert to Equivalent Fractions with Common Denominator 1155

Multiply the numerator and denominator of 12/55 by 21, and multiply the numerator and denominator of 9/21 by 55 so both fractions share the common base 1155.

12 × 21/55 × 21 = 252/1155 and 9 × 55/21 × 55 = 495/1155

Step 3

Add the Numerators

Now add the numerators (252 + 495 = 747) and keep the common denominator 1155 unchanged.

252 + 495/1155 = 747/1155

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 747 and 1155, which is 3. Divide both the numerator and denominator by 3.

747 ÷ 3/1155 ÷ 3 = 249/385

Step 5

Decimal & Percentage Representation

Dividing the numerator 249 by denominator 385 produces a repeating decimal (approximately 0.646753, or 64.6753%).

249 ÷ 385 = 0.646753 (64.6753%)

Visual Representation

The diagram below illustrates 12/55 plus 9/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`249/385`
Mixed Number Form	`249/385`
Decimal Form	`0.646753`
Percentage	`64.6753%`

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Frequently Asked Questions

What is 12/55 plus 9/21 as a fraction?

12/55 + 9/21 in simplest fraction form is 249/385.

What is 12/55 plus 9/21 as a decimal?

12/55 + 9/21 converted to a decimal is 0.646753.

What is 12/55 plus 9/21 as a percentage?

12/55 + 9/21 expressed as a percentage is 64.6753%.

Does 12/55 plus 9/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.646753...) because the denominator contains prime factors other than 2 and 5.