What is 3/15 plus 7/21? (Answer: 8/15)

Exact Answer

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Problem: What is 3/15 plus 7/21?
Formula / Expression: 3/15 + 7/21
Final Answer: 8/15
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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 3/15 by 7, and multiply the numerator and denominator of 7/21 by 5 so both fractions share the common base 105.
Working: 3 × 7/15 × 7 = 21/105 and 7 × 5/21 × 5 = 35/105

Step 3: Add the Numerators
Now add the numerators (21 + 35 = 56) and keep the common denominator 105 unchanged.
Working: 21 + 35/105 = 56/105

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 56 and 105, which is 7. Divide both the numerator and denominator by 7.
Working: 56 ÷ 7/105 ÷ 7 = 8/15

Step 5: Decimal & Percentage Representation
Dividing the numerator 8 by denominator 15 produces a repeating decimal (approximately 0.533333, or 53.3333%).
Working: 8 ÷ 15 = 0.533333 (53.3333%)

Key Values:
- Simplified Fraction: 8/15
- Mixed Number Form: 8/15
- Decimal Value: 0.533333
- Percentage: 53.3333%

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Solved with FractionsCalc:
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3/15 + 7/21 = 8/15

Simplified Fraction

8/15

Mixed Number

Proper (8/15)

Decimal Value

0.533333

Percentage

53.3333%

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Step-by-Step Solution: 3/15 + 7/21

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 3/15 by 7, and multiply the numerator and denominator of 7/21 by 5 so both fractions share the common base 105.

3 × 7/15 × 7 = 21/105 and 7 × 5/21 × 5 = 35/105

Step 3

Add the Numerators

Now add the numerators (21 + 35 = 56) and keep the common denominator 105 unchanged.

21 + 35/105 = 56/105

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 56 and 105, which is 7. Divide both the numerator and denominator by 7.

56 ÷ 7/105 ÷ 7 = 8/15

Step 5

Decimal & Percentage Representation

Dividing the numerator 8 by denominator 15 produces a repeating decimal (approximately 0.533333, or 53.3333%).

8 ÷ 15 = 0.533333 (53.3333%)

Visual Representation

The diagram below illustrates 3/15 plus 7/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`8/15`
Mixed Number Form	`8/15`
Decimal Form	`0.533333`
Percentage	`53.3333%`

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Frequently Asked Questions

What is 3/15 plus 7/21 as a fraction?

3/15 + 7/21 in simplest fraction form is 8/15.

What is 3/15 plus 7/21 as a decimal?

3/15 + 7/21 converted to a decimal is 0.533333.

What is 3/15 plus 7/21 as a percentage?

3/15 + 7/21 expressed as a percentage is 53.3333%.

Does 3/15 plus 7/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.533333...) because the denominator contains prime factors other than 2 and 5.