What is 1/15 plus 12/21? (Answer: 67/105)

Exact Answer

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Problem: What is 1/15 plus 12/21?
Formula / Expression: 1/15 + 12/21
Final Answer: 67/105
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 15 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 105 (which is smaller than their product 15 × 21 = 315, keeping the calculation simpler).
Working: LCD(15, 21) = 105

Step 2: Convert to Equivalent Fractions with Common Denominator 105
Multiply the numerator and denominator of 1/15 by 7, and multiply the numerator and denominator of 12/21 by 5 so both fractions share the common base 105.
Working: 1 × 7/15 × 7 = 7/105 and 12 × 5/21 × 5 = 60/105

Step 3: Add the Numerators
Now add the numerators (7 + 60 = 67) and keep the common denominator 105 unchanged.
Working: 7 + 60/105 = 67/105

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 67 and 105 is 1, confirming that 67/105 cannot be reduced further—it is already in its simplest irreducible form.
Working: 67/105

Step 5: Decimal & Percentage Representation
Dividing the numerator 67 by denominator 105 produces a repeating decimal (approximately 0.638095, or 63.8095%).
Working: 67 ÷ 105 = 0.638095 (63.8095%)

Key Values:
- Simplified Fraction: 67/105
- Mixed Number Form: 67/105
- Decimal Value: 0.638095
- Percentage: 63.8095%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-1-15-plus-12-21/
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1/15 + 12/21 = 67/105

Simplified Fraction

67/105

Mixed Number

Proper (67/105)

Decimal Value

0.638095

Percentage

63.8095%

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Step-by-Step Solution: 1/15 + 12/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 15 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 105 (which is smaller than their product 15 × 21 = 315, keeping the calculation simpler).

LCD(15, 21) = 105

Step 2

Convert to Equivalent Fractions with Common Denominator 105

Multiply the numerator and denominator of 1/15 by 7, and multiply the numerator and denominator of 12/21 by 5 so both fractions share the common base 105.

1 × 7/15 × 7 = 7/105 and 12 × 5/21 × 5 = 60/105

Step 3

Add the Numerators

Now add the numerators (7 + 60 = 67) and keep the common denominator 105 unchanged.

7 + 60/105 = 67/105

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 67 and 105 is 1, confirming that 67/105 cannot be reduced further—it is already in its simplest irreducible form.

67/105

Step 5

Decimal & Percentage Representation

Dividing the numerator 67 by denominator 105 produces a repeating decimal (approximately 0.638095, or 63.8095%).

67 ÷ 105 = 0.638095 (63.8095%)

Visual Representation

The diagram below illustrates 1/15 plus 12/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`67/105`
Mixed Number Form	`67/105`
Decimal Form	`0.638095`
Percentage	`63.8095%`

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Frequently Asked Questions

What is 1/15 plus 12/21 as a fraction?

1/15 + 12/21 in simplest fraction form is 67/105.

What is 1/15 plus 12/21 as a decimal?

1/15 + 12/21 converted to a decimal is 0.638095.

What is 1/15 plus 12/21 as a percentage?

1/15 + 12/21 expressed as a percentage is 63.8095%.

Does 1/15 plus 12/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.638095...) because the denominator contains prime factors other than 2 and 5.