What is 18/35 plus 15/21? (Answer: 43/35)

Exact Answer

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Problem: What is 18/35 plus 15/21?
Formula / Expression: 18/35 + 15/21
Final Answer: 1 8/35 (43/35)
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 35 and 21 share a common factor (GCD = 7). Finding their Least Common Multiple gives an LCD of 105 (which is smaller than their product 35 × 21 = 735, keeping the calculation simpler).
Working: LCD(35, 21) = 105

Step 2: Convert to Equivalent Fractions with Common Denominator 105
Multiply the numerator and denominator of 18/35 by 3, and multiply the numerator and denominator of 15/21 by 5 so both fractions share the common base 105.
Working: 18 × 3/35 × 3 = 54/105 and 15 × 5/21 × 5 = 75/105

Step 3: Add the Numerators
Now add the numerators (54 + 75 = 129) and keep the common denominator 105 unchanged.
Working: 54 + 75/105 = 129/105

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 129 and 105, which is 3. Divide both the numerator and denominator by 3.
Working: 129 ÷ 3/105 ÷ 3 = 43/35

Step 5: Convert Improper Fraction to a Mixed Number
Since the numerator (43) is greater than the denominator (35), divide 43 by 35: it goes in 1 whole time(s) with a remainder of 8, giving the mixed number 1 8/35.
Working: 43/35 = 1 8/35

Step 6: Decimal & Percentage Representation
Dividing the numerator 43 by denominator 35 produces a repeating decimal (approximately 1.228571, or 122.8571%).
Working: 43 ÷ 35 = 1.228571 (122.8571%)

Key Values:
- Simplified Fraction: 43/35
- Mixed Number Form: 1 8/35
- Decimal Value: 1.228571
- Percentage: 122.8571%

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18/35 + 15/21 = 43/35

Simplified Fraction

43/35

Mixed Number

1 8/35

Decimal Value

1.228571

Percentage

122.8571%

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Step-by-Step Solution: 18/35 + 15/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 35 and 21 share a common factor (GCD = 7). Finding their Least Common Multiple gives an LCD of 105 (which is smaller than their product 35 × 21 = 735, keeping the calculation simpler).

LCD(35, 21) = 105

Step 2

Convert to Equivalent Fractions with Common Denominator 105

Multiply the numerator and denominator of 18/35 by 3, and multiply the numerator and denominator of 15/21 by 5 so both fractions share the common base 105.

18 × 3/35 × 3 = 54/105 and 15 × 5/21 × 5 = 75/105

Step 3

Add the Numerators

Now add the numerators (54 + 75 = 129) and keep the common denominator 105 unchanged.

54 + 75/105 = 129/105

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 129 and 105, which is 3. Divide both the numerator and denominator by 3.

129 ÷ 3/105 ÷ 3 = 43/35

Step 5

Convert Improper Fraction to a Mixed Number

Since the numerator (43) is greater than the denominator (35), divide 43 by 35: it goes in 1 whole time(s) with a remainder of 8, giving the mixed number 1 8/35.

43/35 = 18/35

Step 6

Decimal & Percentage Representation

Dividing the numerator 43 by denominator 35 produces a repeating decimal (approximately 1.228571, or 122.8571%).

43 ÷ 35 = 1.228571 (122.8571%)

Visual Representation

The diagram below illustrates 18/35 plus 15/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`43/35`
Mixed Number Form	`1 8/35`
Decimal Form	`1.228571`
Percentage	`122.8571%`

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Frequently Asked Questions

What is 18/35 plus 15/21 as a fraction?

18/35 + 15/21 in simplest fraction form is 43/35 (or 1 8/35 as a mixed number).

What is 18/35 plus 15/21 as a decimal?

18/35 + 15/21 converted to a decimal is 1.228571.

What is 18/35 plus 15/21 as a percentage?

18/35 + 15/21 expressed as a percentage is 122.8571%.

How do you write 18/35 plus 15/21 as a mixed number?

Because the numerator is greater than the denominator, the improper fraction 43/35 can be written as the mixed number 1 8/35.

Does 18/35 plus 15/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 1.228571...) because the denominator contains prime factors other than 2 and 5.