What is 8/51 plus 9/21? (Answer: 209/357)

Exact Answer

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Problem: What is 8/51 plus 9/21?
Formula / Expression: 8/51 + 9/21
Final Answer: 209/357
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 51 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 357 (which is smaller than their product 51 × 21 = 1071, keeping the calculation simpler).
Working: LCD(51, 21) = 357

Step 2: Convert to Equivalent Fractions with Common Denominator 357
Multiply the numerator and denominator of 8/51 by 7, and multiply the numerator and denominator of 9/21 by 17 so both fractions share the common base 357.
Working: 8 × 7/51 × 7 = 56/357 and 9 × 17/21 × 17 = 153/357

Step 3: Add the Numerators
Now add the numerators (56 + 153 = 209) and keep the common denominator 357 unchanged.
Working: 56 + 153/357 = 209/357

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 209 and 357 is 1, confirming that 209/357 cannot be reduced further—it is already in its simplest irreducible form.
Working: 209/357

Step 5: Decimal & Percentage Representation
Dividing the numerator 209 by denominator 357 produces a repeating decimal (approximately 0.585434, or 58.5434%).
Working: 209 ÷ 357 = 0.585434 (58.5434%)

Key Values:
- Simplified Fraction: 209/357
- Mixed Number Form: 209/357
- Decimal Value: 0.585434
- Percentage: 58.5434%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-8-51-plus-9-21/
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8/51 + 9/21 = 209/357

Simplified Fraction

209/357

Mixed Number

Proper (209/357)

Decimal Value

0.585434

Percentage

58.5434%

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Step-by-Step Solution: 8/51 + 9/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 51 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 357 (which is smaller than their product 51 × 21 = 1071, keeping the calculation simpler).

LCD(51, 21) = 357

Step 2

Convert to Equivalent Fractions with Common Denominator 357

Multiply the numerator and denominator of 8/51 by 7, and multiply the numerator and denominator of 9/21 by 17 so both fractions share the common base 357.

8 × 7/51 × 7 = 56/357 and 9 × 17/21 × 17 = 153/357

Step 3

Add the Numerators

Now add the numerators (56 + 153 = 209) and keep the common denominator 357 unchanged.

56 + 153/357 = 209/357

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 209 and 357 is 1, confirming that 209/357 cannot be reduced further—it is already in its simplest irreducible form.

209/357

Step 5

Decimal & Percentage Representation

Dividing the numerator 209 by denominator 357 produces a repeating decimal (approximately 0.585434, or 58.5434%).

209 ÷ 357 = 0.585434 (58.5434%)

Visual Representation

The diagram below illustrates 8/51 plus 9/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`209/357`
Mixed Number Form	`209/357`
Decimal Form	`0.585434`
Percentage	`58.5434%`

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Frequently Asked Questions

What is 8/51 plus 9/21 as a fraction?

8/51 + 9/21 in simplest fraction form is 209/357.

What is 8/51 plus 9/21 as a decimal?

8/51 + 9/21 converted to a decimal is 0.585434.

What is 8/51 plus 9/21 as a percentage?

8/51 + 9/21 expressed as a percentage is 58.5434%.

Does 8/51 plus 9/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.585434...) because the denominator contains prime factors other than 2 and 5.