What is 8/57 plus 5/21? (Answer: 151/399)

Exact Answer

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Problem: What is 8/57 plus 5/21?
Formula / Expression: 8/57 + 5/21
Final Answer: 151/399
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 57 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 399 (which is smaller than their product 57 × 21 = 1197, keeping the calculation simpler).
Working: LCD(57, 21) = 399

Step 2: Convert to Equivalent Fractions with Common Denominator 399
Multiply the numerator and denominator of 8/57 by 7, and multiply the numerator and denominator of 5/21 by 19 so both fractions share the common base 399.
Working: 8 × 7/57 × 7 = 56/399 and 5 × 19/21 × 19 = 95/399

Step 3: Add the Numerators
Now add the numerators (56 + 95 = 151) and keep the common denominator 399 unchanged.
Working: 56 + 95/399 = 151/399

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 151 and 399 is 1, confirming that 151/399 cannot be reduced further—it is already in its simplest irreducible form.
Working: 151/399

Step 5: Decimal & Percentage Representation
Dividing the numerator 151 by denominator 399 produces a repeating decimal (approximately 0.378446, or 37.8446%).
Working: 151 ÷ 399 = 0.378446 (37.8446%)

Key Values:
- Simplified Fraction: 151/399
- Mixed Number Form: 151/399
- Decimal Value: 0.378446
- Percentage: 37.8446%

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Solved with FractionsCalc:
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8/57 + 5/21 = 151/399

Simplified Fraction

151/399

Mixed Number

Proper (151/399)

Decimal Value

0.378446

Percentage

37.8446%

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Step-by-Step Solution: 8/57 + 5/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 57 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 399 (which is smaller than their product 57 × 21 = 1197, keeping the calculation simpler).

LCD(57, 21) = 399

Step 2

Convert to Equivalent Fractions with Common Denominator 399

Multiply the numerator and denominator of 8/57 by 7, and multiply the numerator and denominator of 5/21 by 19 so both fractions share the common base 399.

8 × 7/57 × 7 = 56/399 and 5 × 19/21 × 19 = 95/399

Step 3

Add the Numerators

Now add the numerators (56 + 95 = 151) and keep the common denominator 399 unchanged.

56 + 95/399 = 151/399

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 151 and 399 is 1, confirming that 151/399 cannot be reduced further—it is already in its simplest irreducible form.

151/399

Step 5

Decimal & Percentage Representation

Dividing the numerator 151 by denominator 399 produces a repeating decimal (approximately 0.378446, or 37.8446%).

151 ÷ 399 = 0.378446 (37.8446%)

Visual Representation

The diagram below illustrates 8/57 plus 5/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`151/399`
Mixed Number Form	`151/399`
Decimal Form	`0.378446`
Percentage	`37.8446%`

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Frequently Asked Questions

What is 8/57 plus 5/21 as a fraction?

8/57 + 5/21 in simplest fraction form is 151/399.

What is 8/57 plus 5/21 as a decimal?

8/57 + 5/21 converted to a decimal is 0.378446.

What is 8/57 plus 5/21 as a percentage?

8/57 + 5/21 expressed as a percentage is 37.8446%.

Does 8/57 plus 5/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.378446...) because the denominator contains prime factors other than 2 and 5.