What is 5/42 plus 9/21? (Answer: 23/42)

Exact Answer

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Problem: What is 5/42 plus 9/21?
Formula / Expression: 5/42 + 9/21
Final Answer: 23/42
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
Notice that 42 is an exact multiple of 21 (21 × 2 = 42). The Least Common Denominator (LCD) is simply 42, meaning we only need to scale one fraction.
Working: LCD(42, 21) = 42

Step 2: Convert to Equivalent Fractions with Common Denominator 42
Multiply the numerator and denominator of 5/42 by 1, and multiply the numerator and denominator of 9/21 by 2 so both fractions share the common base 42.
Working: 5 × 1/42 × 1 = 5/42 and 9 × 2/21 × 2 = 18/42

Step 3: Add the Numerators
Now add the numerators (5 + 18 = 23) and keep the common denominator 42 unchanged.
Working: 5 + 18/42 = 23/42

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 23 and 42 is 1, confirming that 23/42 cannot be reduced further—it is already in its simplest irreducible form.
Working: 23/42

Step 5: Decimal & Percentage Representation
Dividing the numerator 23 by denominator 42 produces a repeating decimal (approximately 0.547619, or 54.7619%).
Working: 23 ÷ 42 = 0.547619 (54.7619%)

Key Values:
- Simplified Fraction: 23/42
- Mixed Number Form: 23/42
- Decimal Value: 0.547619
- Percentage: 54.7619%

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Solved with FractionsCalc:
https://fractionscalc.com/what-is-5-42-plus-9-21/
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5/42 + 9/21 = 23/42

Simplified Fraction

23/42

Mixed Number

Proper (23/42)

Decimal Value

0.547619

Percentage

54.7619%

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Step-by-Step Solution: 5/42 + 9/21

Step 1

Find the Least Common Denominator (LCD)

Notice that 42 is an exact multiple of 21 (21 × 2 = 42). The Least Common Denominator (LCD) is simply 42, meaning we only need to scale one fraction.

LCD(42, 21) = 42

Step 2

Convert to Equivalent Fractions with Common Denominator 42

Multiply the numerator and denominator of 5/42 by 1, and multiply the numerator and denominator of 9/21 by 2 so both fractions share the common base 42.

5 × 1/42 × 1 = 5/42 and 9 × 2/21 × 2 = 18/42

Step 3

Add the Numerators

Now add the numerators (5 + 18 = 23) and keep the common denominator 42 unchanged.

5 + 18/42 = 23/42

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 23 and 42 is 1, confirming that 23/42 cannot be reduced further—it is already in its simplest irreducible form.

23/42

Step 5

Decimal & Percentage Representation

Dividing the numerator 23 by denominator 42 produces a repeating decimal (approximately 0.547619, or 54.7619%).

23 ÷ 42 = 0.547619 (54.7619%)

Visual Representation

The diagram below illustrates 5/42 plus 9/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`23/42`
Mixed Number Form	`23/42`
Decimal Form	`0.547619`
Percentage	`54.7619%`

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Frequently Asked Questions

What is 5/42 plus 9/21 as a fraction?

5/42 + 9/21 in simplest fraction form is 23/42.

What is 5/42 plus 9/21 as a decimal?

5/42 + 9/21 converted to a decimal is 0.547619.

What is 5/42 plus 9/21 as a percentage?

5/42 + 9/21 expressed as a percentage is 54.7619%.

Does 5/42 plus 9/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.547619...) because the denominator contains prime factors other than 2 and 5.