What is 13/31 plus 12/21? (Answer: 215/217)

Exact Answer

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Problem: What is 13/31 plus 12/21?
Formula / Expression: 13/31 + 12/21
Final Answer: 215/217
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 31 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 31 × 21 = 651.
Working: LCD(31, 21) = 651

Step 2: Convert to Equivalent Fractions with Common Denominator 651
Multiply the numerator and denominator of 13/31 by 21, and multiply the numerator and denominator of 12/21 by 31 so both fractions share the common base 651.
Working: 13 × 21/31 × 21 = 273/651 and 12 × 31/21 × 31 = 372/651

Step 3: Add the Numerators
Now add the numerators (273 + 372 = 645) and keep the common denominator 651 unchanged.
Working: 273 + 372/651 = 645/651

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 645 and 651, which is 3. Divide both the numerator and denominator by 3.
Working: 645 ÷ 3/651 ÷ 3 = 215/217

Step 5: Decimal & Percentage Representation
Dividing the numerator 215 by denominator 217 produces a repeating decimal (approximately 0.990783, or 99.0783%).
Working: 215 ÷ 217 = 0.990783 (99.0783%)

Key Values:
- Simplified Fraction: 215/217
- Mixed Number Form: 215/217
- Decimal Value: 0.990783
- Percentage: 99.0783%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-13-31-plus-12-21/
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13/31 + 12/21 = 215/217

Simplified Fraction

215/217

Mixed Number

Proper (215/217)

Decimal Value

0.990783

Percentage

99.0783%

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Step-by-Step Solution: 13/31 + 12/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 31 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 31 × 21 = 651.

LCD(31, 21) = 651

Step 2

Convert to Equivalent Fractions with Common Denominator 651

Multiply the numerator and denominator of 13/31 by 21, and multiply the numerator and denominator of 12/21 by 31 so both fractions share the common base 651.

13 × 21/31 × 21 = 273/651 and 12 × 31/21 × 31 = 372/651

Step 3

Add the Numerators

Now add the numerators (273 + 372 = 645) and keep the common denominator 651 unchanged.

273 + 372/651 = 645/651

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 645 and 651, which is 3. Divide both the numerator and denominator by 3.

645 ÷ 3/651 ÷ 3 = 215/217

Step 5

Decimal & Percentage Representation

Dividing the numerator 215 by denominator 217 produces a repeating decimal (approximately 0.990783, or 99.0783%).

215 ÷ 217 = 0.990783 (99.0783%)

Visual Representation

The diagram below illustrates 13/31 plus 12/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`215/217`
Mixed Number Form	`215/217`
Decimal Form	`0.990783`
Percentage	`99.0783%`

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Frequently Asked Questions

What is 13/31 plus 12/21 as a fraction?

13/31 + 12/21 in simplest fraction form is 215/217.

What is 13/31 plus 12/21 as a decimal?

13/31 + 12/21 converted to a decimal is 0.990783.

What is 13/31 plus 12/21 as a percentage?

13/31 + 12/21 expressed as a percentage is 99.0783%.

Does 13/31 plus 12/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.990783...) because the denominator contains prime factors other than 2 and 5.