What is 5/9 minus 9/21? (Answer: 8/63)

Exact Answer

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Problem: What is 5/9 minus 9/21?
Formula / Expression: 5/9 − 9/21
Final Answer: 8/63
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 9 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 63 (which is smaller than their product 9 × 21 = 189, keeping the calculation simpler).
Working: LCD(9, 21) = 63

Step 2: Convert to Equivalent Fractions with Common Denominator 63
Multiply the numerator and denominator of 5/9 by 7, and multiply the numerator and denominator of 9/21 by 3 so both fractions share the common base 63.
Working: 5 × 7/9 × 7 = 35/63 and 9 × 3/21 × 3 = 27/63

Step 3: Subtract the Numerators
Now subtract the numerators (35 − 27 = 8) and keep the common denominator 63 unchanged.
Working: 35 − 27/63 = 8/63

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 8 and 63 is 1, confirming that 8/63 cannot be reduced further—it is already in its simplest irreducible form.
Working: 8/63

Step 5: Decimal & Percentage Representation
Dividing the numerator 8 by denominator 63 produces a repeating decimal (approximately 0.126984, or 12.6984%).
Working: 8 ÷ 63 = 0.126984 (12.6984%)

Key Values:
- Simplified Fraction: 8/63
- Mixed Number Form: 8/63
- Decimal Value: 0.126984
- Percentage: 12.6984%

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5/9 − 9/21 = 8/63

Simplified Fraction

8/63

Mixed Number

Proper (8/63)

Decimal Value

0.126984

Percentage

12.6984%

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Step-by-Step Solution: 5/9 − 9/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 9 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 63 (which is smaller than their product 9 × 21 = 189, keeping the calculation simpler).

LCD(9, 21) = 63

Step 2

Convert to Equivalent Fractions with Common Denominator 63

Multiply the numerator and denominator of 5/9 by 7, and multiply the numerator and denominator of 9/21 by 3 so both fractions share the common base 63.

5 × 7/9 × 7 = 35/63 and 9 × 3/21 × 3 = 27/63

Step 3

Subtract the Numerators

Now subtract the numerators (35 − 27 = 8) and keep the common denominator 63 unchanged.

35 − 27/63 = 8/63

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 8 and 63 is 1, confirming that 8/63 cannot be reduced further—it is already in its simplest irreducible form.

8/63

Step 5

Decimal & Percentage Representation

Dividing the numerator 8 by denominator 63 produces a repeating decimal (approximately 0.126984, or 12.6984%).

8 ÷ 63 = 0.126984 (12.6984%)

Visual Representation

The diagram below illustrates 5/9 minus 9/21 visually:

−

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`8/63`
Mixed Number Form	`8/63`
Decimal Form	`0.126984`
Percentage	`12.6984%`

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Frequently Asked Questions

What is 5/9 minus 9/21 as a fraction?

5/9 − 9/21 in simplest fraction form is 8/63.

What is 5/9 minus 9/21 as a decimal?

5/9 − 9/21 converted to a decimal is 0.126984.

What is 5/9 minus 9/21 as a percentage?

5/9 − 9/21 expressed as a percentage is 12.6984%.

Does 5/9 minus 9/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.126984...) because the denominator contains prime factors other than 2 and 5.