What is 5/19 plus 8/21? (Answer: 257/399)

Exact Answer

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Problem: What is 5/19 plus 8/21?
Formula / Expression: 5/19 + 8/21
Final Answer: 257/399
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 19 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 19 × 21 = 399.
Working: LCD(19, 21) = 399

Step 2: Convert to Equivalent Fractions with Common Denominator 399
Multiply the numerator and denominator of 5/19 by 21, and multiply the numerator and denominator of 8/21 by 19 so both fractions share the common base 399.
Working: 5 × 21/19 × 21 = 105/399 and 8 × 19/21 × 19 = 152/399

Step 3: Add the Numerators
Now add the numerators (105 + 152 = 257) and keep the common denominator 399 unchanged.
Working: 105 + 152/399 = 257/399

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 257 and 399 is 1, confirming that 257/399 cannot be reduced further—it is already in its simplest irreducible form.
Working: 257/399

Step 5: Decimal & Percentage Representation
Dividing the numerator 257 by denominator 399 produces a repeating decimal (approximately 0.64411, or 64.411%).
Working: 257 ÷ 399 = 0.64411 (64.411%)

Key Values:
- Simplified Fraction: 257/399
- Mixed Number Form: 257/399
- Decimal Value: 0.64411
- Percentage: 64.411%

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Solved with FractionsCalc:
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5/19 + 8/21 = 257/399

Simplified Fraction

257/399

Mixed Number

Proper (257/399)

Decimal Value

0.64411

Percentage

64.411%

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Step-by-Step Solution: 5/19 + 8/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 19 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 19 × 21 = 399.

LCD(19, 21) = 399

Step 2

Convert to Equivalent Fractions with Common Denominator 399

Multiply the numerator and denominator of 5/19 by 21, and multiply the numerator and denominator of 8/21 by 19 so both fractions share the common base 399.

5 × 21/19 × 21 = 105/399 and 8 × 19/21 × 19 = 152/399

Step 3

Add the Numerators

Now add the numerators (105 + 152 = 257) and keep the common denominator 399 unchanged.

105 + 152/399 = 257/399

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 257 and 399 is 1, confirming that 257/399 cannot be reduced further—it is already in its simplest irreducible form.

257/399

Step 5

Decimal & Percentage Representation

Dividing the numerator 257 by denominator 399 produces a repeating decimal (approximately 0.64411, or 64.411%).

257 ÷ 399 = 0.64411 (64.411%)

Visual Representation

The diagram below illustrates 5/19 plus 8/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`257/399`
Mixed Number Form	`257/399`
Decimal Form	`0.64411`
Percentage	`64.411%`

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Frequently Asked Questions

What is 5/19 plus 8/21 as a fraction?

5/19 + 8/21 in simplest fraction form is 257/399.

What is 5/19 plus 8/21 as a decimal?

5/19 + 8/21 converted to a decimal is 0.64411.

What is 5/19 plus 8/21 as a percentage?

5/19 + 8/21 expressed as a percentage is 64.411%.

Does 5/19 plus 8/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.64411...) because the denominator contains prime factors other than 2 and 5.