What is 18/38 plus 15/21? (Answer: 158/133)

Exact Answer

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Problem: What is 18/38 plus 15/21?
Formula / Expression: 18/38 + 15/21
Final Answer: 1 25/133 (158/133)
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 38 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 38 × 21 = 798.
Working: LCD(38, 21) = 798

Step 2: Convert to Equivalent Fractions with Common Denominator 798
Multiply the numerator and denominator of 18/38 by 21, and multiply the numerator and denominator of 15/21 by 38 so both fractions share the common base 798.
Working: 18 × 21/38 × 21 = 378/798 and 15 × 38/21 × 38 = 570/798

Step 3: Add the Numerators
Now add the numerators (378 + 570 = 948) and keep the common denominator 798 unchanged.
Working: 378 + 570/798 = 948/798

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 948 and 798, which is 6. Divide both the numerator and denominator by 6.
Working: 948 ÷ 6/798 ÷ 6 = 158/133

Step 5: Convert Improper Fraction to a Mixed Number
Since the numerator (158) is greater than the denominator (133), divide 158 by 133: it goes in 1 whole time(s) with a remainder of 25, giving the mixed number 1 25/133.
Working: 158/133 = 1 25/133

Step 6: Decimal & Percentage Representation
Dividing the numerator 158 by denominator 133 produces a repeating decimal (approximately 1.18797, or 118.797%).
Working: 158 ÷ 133 = 1.18797 (118.797%)

Key Values:
- Simplified Fraction: 158/133
- Mixed Number Form: 1 25/133
- Decimal Value: 1.18797
- Percentage: 118.797%

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Solved with FractionsCalc:
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18/38 + 15/21 = 158/133

Simplified Fraction

158/133

Mixed Number

1 25/133

Decimal Value

1.18797

Percentage

118.797%

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Step-by-Step Solution: 18/38 + 15/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 38 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 38 × 21 = 798.

LCD(38, 21) = 798

Step 2

Convert to Equivalent Fractions with Common Denominator 798

Multiply the numerator and denominator of 18/38 by 21, and multiply the numerator and denominator of 15/21 by 38 so both fractions share the common base 798.

18 × 21/38 × 21 = 378/798 and 15 × 38/21 × 38 = 570/798

Step 3

Add the Numerators

Now add the numerators (378 + 570 = 948) and keep the common denominator 798 unchanged.

378 + 570/798 = 948/798

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 948 and 798, which is 6. Divide both the numerator and denominator by 6.

948 ÷ 6/798 ÷ 6 = 158/133

Step 5

Convert Improper Fraction to a Mixed Number

Since the numerator (158) is greater than the denominator (133), divide 158 by 133: it goes in 1 whole time(s) with a remainder of 25, giving the mixed number 1 25/133.

158/133 = 125/133

Step 6

Decimal & Percentage Representation

Dividing the numerator 158 by denominator 133 produces a repeating decimal (approximately 1.18797, or 118.797%).

158 ÷ 133 = 1.18797 (118.797%)

Visual Representation

The diagram below illustrates 18/38 plus 15/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`158/133`
Mixed Number Form	`1 25/133`
Decimal Form	`1.18797`
Percentage	`118.797%`

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Frequently Asked Questions

What is 18/38 plus 15/21 as a fraction?

18/38 + 15/21 in simplest fraction form is 158/133 (or 1 25/133 as a mixed number).

What is 18/38 plus 15/21 as a decimal?

18/38 + 15/21 converted to a decimal is 1.18797.

What is 18/38 plus 15/21 as a percentage?

18/38 + 15/21 expressed as a percentage is 118.797%.

How do you write 18/38 plus 15/21 as a mixed number?

Because the numerator is greater than the denominator, the improper fraction 158/133 can be written as the mixed number 1 25/133.

Does 18/38 plus 15/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 1.18797...) because the denominator contains prime factors other than 2 and 5.