What is 1/9 minus 5/21? (Answer: -8/63)

Exact Answer

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Problem: What is 1/9 minus 5/21?
Formula / Expression: 1/9 − 5/21
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 1/9 by 7, and multiply the numerator and denominator of 5/21 by 3 so both fractions share the common base 63.
Working: 1 × 7/9 × 7 = 7/63 and 5 × 3/21 × 3 = 15/63

Step 3: Subtract the Numerators
Now subtract the numerators (7 − 15 = -8) and keep the common denominator 63 unchanged.
Working: 7 − 15/63 = -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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Solved with FractionsCalc:
https://fractionscalc.com/what-is-1-9-minus-5-21/
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1/9 − 5/21 = -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: 1/9 − 5/21

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 1/9 by 7, and multiply the numerator and denominator of 5/21 by 3 so both fractions share the common base 63.

1 × 7/9 × 7 = 7/63 and 5 × 3/21 × 3 = 15/63

Step 3

Subtract the Numerators

Now subtract the numerators (7 − 15 = -8) and keep the common denominator 63 unchanged.

7 − 15/63 = -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 1/9 minus 5/21 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 1/9 minus 5/21 as a fraction?

1/9 − 5/21 in simplest fraction form is -8/63.

What is 1/9 minus 5/21 as a decimal?

1/9 − 5/21 converted to a decimal is -0.126984.

What is 1/9 minus 5/21 as a percentage?

1/9 − 5/21 expressed as a percentage is -12.6984%.

Does 1/9 minus 5/21 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.