What is 18/26 plus 15/21? (Answer: 128/91)

Exact Answer

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Problem: What is 18/26 plus 15/21?
Formula / Expression: 18/26 + 15/21
Final Answer: 1 37/91 (128/91)
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 26 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 26 × 21 = 546.
Working: LCD(26, 21) = 546

Step 2: Convert to Equivalent Fractions with Common Denominator 546
Multiply the numerator and denominator of 18/26 by 21, and multiply the numerator and denominator of 15/21 by 26 so both fractions share the common base 546.
Working: 18 × 21/26 × 21 = 378/546 and 15 × 26/21 × 26 = 390/546

Step 3: Add the Numerators
Now add the numerators (378 + 390 = 768) and keep the common denominator 546 unchanged.
Working: 378 + 390/546 = 768/546

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 768 and 546, which is 6. Divide both the numerator and denominator by 6.
Working: 768 ÷ 6/546 ÷ 6 = 128/91

Step 5: Convert Improper Fraction to a Mixed Number
Since the numerator (128) is greater than the denominator (91), divide 128 by 91: it goes in 1 whole time(s) with a remainder of 37, giving the mixed number 1 37/91.
Working: 128/91 = 1 37/91

Step 6: Decimal & Percentage Representation
Dividing the numerator 128 by denominator 91 produces a repeating decimal (approximately 1.406593, or 140.6593%).
Working: 128 ÷ 91 = 1.406593 (140.6593%)

Key Values:
- Simplified Fraction: 128/91
- Mixed Number Form: 1 37/91
- Decimal Value: 1.406593
- Percentage: 140.6593%

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Solved with FractionsCalc:
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18/26 + 15/21 = 128/91

Simplified Fraction

128/91

Mixed Number

1 37/91

Decimal Value

1.406593

Percentage

140.6593%

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Step-by-Step Solution: 18/26 + 15/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 26 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 26 × 21 = 546.

LCD(26, 21) = 546

Step 2

Convert to Equivalent Fractions with Common Denominator 546

Multiply the numerator and denominator of 18/26 by 21, and multiply the numerator and denominator of 15/21 by 26 so both fractions share the common base 546.

18 × 21/26 × 21 = 378/546 and 15 × 26/21 × 26 = 390/546

Step 3

Add the Numerators

Now add the numerators (378 + 390 = 768) and keep the common denominator 546 unchanged.

378 + 390/546 = 768/546

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 768 and 546, which is 6. Divide both the numerator and denominator by 6.

768 ÷ 6/546 ÷ 6 = 128/91

Step 5

Convert Improper Fraction to a Mixed Number

Since the numerator (128) is greater than the denominator (91), divide 128 by 91: it goes in 1 whole time(s) with a remainder of 37, giving the mixed number 1 37/91.

128/91 = 137/91

Step 6

Decimal & Percentage Representation

Dividing the numerator 128 by denominator 91 produces a repeating decimal (approximately 1.406593, or 140.6593%).

128 ÷ 91 = 1.406593 (140.6593%)

Visual Representation

The diagram below illustrates 18/26 plus 15/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`128/91`
Mixed Number Form	`1 37/91`
Decimal Form	`1.406593`
Percentage	`140.6593%`

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Frequently Asked Questions

What is 18/26 plus 15/21 as a fraction?

18/26 + 15/21 in simplest fraction form is 128/91 (or 1 37/91 as a mixed number).

What is 18/26 plus 15/21 as a decimal?

18/26 + 15/21 converted to a decimal is 1.406593.

What is 18/26 plus 15/21 as a percentage?

18/26 + 15/21 expressed as a percentage is 140.6593%.

How do you write 18/26 plus 15/21 as a mixed number?

Because the numerator is greater than the denominator, the improper fraction 128/91 can be written as the mixed number 1 37/91.

Does 18/26 plus 15/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 1.406593...) because the denominator contains prime factors other than 2 and 5.