What is 12/39 plus 7/21? (Answer: 25/39)

Exact Answer

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Problem: What is 12/39 plus 7/21?
Formula / Expression: 12/39 + 7/21
Final Answer: 25/39
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 39 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 273 (which is smaller than their product 39 × 21 = 819, keeping the calculation simpler).
Working: LCD(39, 21) = 273

Step 2: Convert to Equivalent Fractions with Common Denominator 273
Multiply the numerator and denominator of 12/39 by 7, and multiply the numerator and denominator of 7/21 by 13 so both fractions share the common base 273.
Working: 12 × 7/39 × 7 = 84/273 and 7 × 13/21 × 13 = 91/273

Step 3: Add the Numerators
Now add the numerators (84 + 91 = 175) and keep the common denominator 273 unchanged.
Working: 84 + 91/273 = 175/273

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 175 and 273, which is 7. Divide both the numerator and denominator by 7.
Working: 175 ÷ 7/273 ÷ 7 = 25/39

Step 5: Decimal & Percentage Representation
Dividing the numerator 25 by denominator 39 produces a repeating decimal (approximately 0.641026, or 64.1026%).
Working: 25 ÷ 39 = 0.641026 (64.1026%)

Key Values:
- Simplified Fraction: 25/39
- Mixed Number Form: 25/39
- Decimal Value: 0.641026
- Percentage: 64.1026%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-12-39-plus-7-21/
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12/39 + 7/21 = 25/39

Simplified Fraction

25/39

Mixed Number

Proper (25/39)

Decimal Value

0.641026

Percentage

64.1026%

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Step-by-Step Solution: 12/39 + 7/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 39 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 273 (which is smaller than their product 39 × 21 = 819, keeping the calculation simpler).

LCD(39, 21) = 273

Step 2

Convert to Equivalent Fractions with Common Denominator 273

Multiply the numerator and denominator of 12/39 by 7, and multiply the numerator and denominator of 7/21 by 13 so both fractions share the common base 273.

12 × 7/39 × 7 = 84/273 and 7 × 13/21 × 13 = 91/273

Step 3

Add the Numerators

Now add the numerators (84 + 91 = 175) and keep the common denominator 273 unchanged.

84 + 91/273 = 175/273

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 175 and 273, which is 7. Divide both the numerator and denominator by 7.

175 ÷ 7/273 ÷ 7 = 25/39

Step 5

Decimal & Percentage Representation

Dividing the numerator 25 by denominator 39 produces a repeating decimal (approximately 0.641026, or 64.1026%).

25 ÷ 39 = 0.641026 (64.1026%)

Visual Representation

The diagram below illustrates 12/39 plus 7/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`25/39`
Mixed Number Form	`25/39`
Decimal Form	`0.641026`
Percentage	`64.1026%`

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Frequently Asked Questions

What is 12/39 plus 7/21 as a fraction?

12/39 + 7/21 in simplest fraction form is 25/39.

What is 12/39 plus 7/21 as a decimal?

12/39 + 7/21 converted to a decimal is 0.641026.

What is 12/39 plus 7/21 as a percentage?

12/39 + 7/21 expressed as a percentage is 64.1026%.

Does 12/39 plus 7/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.641026...) because the denominator contains prime factors other than 2 and 5.