What is 15/45 plus 8/21? (Answer: 5/7)

Exact Answer

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Problem: What is 15/45 plus 8/21?
Formula / Expression: 15/45 + 8/21
Final Answer: 5/7
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 45 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 315 (which is smaller than their product 45 × 21 = 945, keeping the calculation simpler).
Working: LCD(45, 21) = 315

Step 2: Convert to Equivalent Fractions with Common Denominator 315
Multiply the numerator and denominator of 15/45 by 7, and multiply the numerator and denominator of 8/21 by 15 so both fractions share the common base 315.
Working: 15 × 7/45 × 7 = 105/315 and 8 × 15/21 × 15 = 120/315

Step 3: Add the Numerators
Now add the numerators (105 + 120 = 225) and keep the common denominator 315 unchanged.
Working: 105 + 120/315 = 225/315

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 225 and 315, which is 45. Divide both the numerator and denominator by 45.
Working: 225 ÷ 45/315 ÷ 45 = 5/7

Step 5: Decimal & Percentage Representation
Dividing the numerator 5 by denominator 7 produces a repeating decimal (approximately 0.714286, or 71.4286%).
Working: 5 ÷ 7 = 0.714286 (71.4286%)

Key Values:
- Simplified Fraction: 5/7
- Mixed Number Form: 5/7
- Decimal Value: 0.714286
- Percentage: 71.4286%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-15-45-plus-8-21/
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15/45 + 8/21 = 5/7

Simplified Fraction

5/7

Mixed Number

Proper (5/7)

Decimal Value

0.714286

Percentage

71.4286%

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Step-by-Step Solution: 15/45 + 8/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 45 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 315 (which is smaller than their product 45 × 21 = 945, keeping the calculation simpler).

LCD(45, 21) = 315

Step 2

Convert to Equivalent Fractions with Common Denominator 315

Multiply the numerator and denominator of 15/45 by 7, and multiply the numerator and denominator of 8/21 by 15 so both fractions share the common base 315.

15 × 7/45 × 7 = 105/315 and 8 × 15/21 × 15 = 120/315

Step 3

Add the Numerators

Now add the numerators (105 + 120 = 225) and keep the common denominator 315 unchanged.

105 + 120/315 = 225/315

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 225 and 315, which is 45. Divide both the numerator and denominator by 45.

225 ÷ 45/315 ÷ 45 = 5/7

Step 5

Decimal & Percentage Representation

Dividing the numerator 5 by denominator 7 produces a repeating decimal (approximately 0.714286, or 71.4286%).

5 ÷ 7 = 0.714286 (71.4286%)

Visual Representation

The diagram below illustrates 15/45 plus 8/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`5/7`
Mixed Number Form	`5/7`
Decimal Form	`0.714286`
Percentage	`71.4286%`

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Frequently Asked Questions

What is 15/45 plus 8/21 as a fraction?

15/45 + 8/21 in simplest fraction form is 5/7.

What is 15/45 plus 8/21 as a decimal?

15/45 + 8/21 converted to a decimal is 0.714286.

What is 15/45 plus 8/21 as a percentage?

15/45 + 8/21 expressed as a percentage is 71.4286%.

Does 15/45 plus 8/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.714286...) because the denominator contains prime factors other than 2 and 5.