What is 9/30 plus 8/21? (Answer: 143/210)

Exact Answer

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Problem: What is 9/30 plus 8/21?
Formula / Expression: 9/30 + 8/21
Final Answer: 143/210
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 30 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 210 (which is smaller than their product 30 × 21 = 630, keeping the calculation simpler).
Working: LCD(30, 21) = 210

Step 2: Convert to Equivalent Fractions with Common Denominator 210
Multiply the numerator and denominator of 9/30 by 7, and multiply the numerator and denominator of 8/21 by 10 so both fractions share the common base 210.
Working: 9 × 7/30 × 7 = 63/210 and 8 × 10/21 × 10 = 80/210

Step 3: Add the Numerators
Now add the numerators (63 + 80 = 143) and keep the common denominator 210 unchanged.
Working: 63 + 80/210 = 143/210

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 143 and 210 is 1, confirming that 143/210 cannot be reduced further—it is already in its simplest irreducible form.
Working: 143/210

Step 5: Decimal & Percentage Representation
Dividing the numerator 143 by denominator 210 produces a repeating decimal (approximately 0.680952, or 68.0952%).
Working: 143 ÷ 210 = 0.680952 (68.0952%)

Key Values:
- Simplified Fraction: 143/210
- Mixed Number Form: 143/210
- Decimal Value: 0.680952
- Percentage: 68.0952%

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9/30 + 8/21 = 143/210

Simplified Fraction

143/210

Mixed Number

Proper (143/210)

Decimal Value

0.680952

Percentage

68.0952%

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Step-by-Step Solution: 9/30 + 8/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 30 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 210 (which is smaller than their product 30 × 21 = 630, keeping the calculation simpler).

LCD(30, 21) = 210

Step 2

Convert to Equivalent Fractions with Common Denominator 210

Multiply the numerator and denominator of 9/30 by 7, and multiply the numerator and denominator of 8/21 by 10 so both fractions share the common base 210.

9 × 7/30 × 7 = 63/210 and 8 × 10/21 × 10 = 80/210

Step 3

Add the Numerators

Now add the numerators (63 + 80 = 143) and keep the common denominator 210 unchanged.

63 + 80/210 = 143/210

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 143 and 210 is 1, confirming that 143/210 cannot be reduced further—it is already in its simplest irreducible form.

143/210

Step 5

Decimal & Percentage Representation

Dividing the numerator 143 by denominator 210 produces a repeating decimal (approximately 0.680952, or 68.0952%).

143 ÷ 210 = 0.680952 (68.0952%)

Visual Representation

The diagram below illustrates 9/30 plus 8/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`143/210`
Mixed Number Form	`143/210`
Decimal Form	`0.680952`
Percentage	`68.0952%`

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Frequently Asked Questions

What is 9/30 plus 8/21 as a fraction?

9/30 + 8/21 in simplest fraction form is 143/210.

What is 9/30 plus 8/21 as a decimal?

9/30 + 8/21 converted to a decimal is 0.680952.

What is 9/30 plus 8/21 as a percentage?

9/30 + 8/21 expressed as a percentage is 68.0952%.

Does 9/30 plus 8/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.680952...) because the denominator contains prime factors other than 2 and 5.