What is 3/39 plus 15/21? (Answer: 72/91)

Exact Answer

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Problem: What is 3/39 plus 15/21?
Formula / Expression: 3/39 + 15/21
Final Answer: 72/91
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 39 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 273 (which is smaller than their product 39 × 21 = 819, keeping the calculation simpler).
Working: LCD(39, 21) = 273

Step 2: Convert to Equivalent Fractions with Common Denominator 273
Multiply the numerator and denominator of 3/39 by 7, and multiply the numerator and denominator of 15/21 by 13 so both fractions share the common base 273.
Working: 3 × 7/39 × 7 = 21/273 and 15 × 13/21 × 13 = 195/273

Step 3: Add the Numerators
Now add the numerators (21 + 195 = 216) and keep the common denominator 273 unchanged.
Working: 21 + 195/273 = 216/273

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 216 and 273, which is 3. Divide both the numerator and denominator by 3.
Working: 216 ÷ 3/273 ÷ 3 = 72/91

Step 5: Decimal & Percentage Representation
Dividing the numerator 72 by denominator 91 produces a repeating decimal (approximately 0.791209, or 79.1209%).
Working: 72 ÷ 91 = 0.791209 (79.1209%)

Key Values:
- Simplified Fraction: 72/91
- Mixed Number Form: 72/91
- Decimal Value: 0.791209
- Percentage: 79.1209%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-3-39-plus-15-21/
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3/39 + 15/21 = 72/91

Simplified Fraction

72/91

Mixed Number

Proper (72/91)

Decimal Value

0.791209

Percentage

79.1209%

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Step-by-Step Solution: 3/39 + 15/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 39 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 273 (which is smaller than their product 39 × 21 = 819, keeping the calculation simpler).

LCD(39, 21) = 273

Step 2

Convert to Equivalent Fractions with Common Denominator 273

Multiply the numerator and denominator of 3/39 by 7, and multiply the numerator and denominator of 15/21 by 13 so both fractions share the common base 273.

3 × 7/39 × 7 = 21/273 and 15 × 13/21 × 13 = 195/273

Step 3

Add the Numerators

Now add the numerators (21 + 195 = 216) and keep the common denominator 273 unchanged.

21 + 195/273 = 216/273

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 216 and 273, which is 3. Divide both the numerator and denominator by 3.

216 ÷ 3/273 ÷ 3 = 72/91

Step 5

Decimal & Percentage Representation

Dividing the numerator 72 by denominator 91 produces a repeating decimal (approximately 0.791209, or 79.1209%).

72 ÷ 91 = 0.791209 (79.1209%)

Visual Representation

The diagram below illustrates 3/39 plus 15/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`72/91`
Mixed Number Form	`72/91`
Decimal Form	`0.791209`
Percentage	`79.1209%`

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Frequently Asked Questions

What is 3/39 plus 15/21 as a fraction?

3/39 + 15/21 in simplest fraction form is 72/91.

What is 3/39 plus 15/21 as a decimal?

3/39 + 15/21 converted to a decimal is 0.791209.

What is 3/39 plus 15/21 as a percentage?

3/39 + 15/21 expressed as a percentage is 79.1209%.

Does 3/39 plus 15/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.791209...) because the denominator contains prime factors other than 2 and 5.