What is 4/21 plus 2/7? (Answer: 10/21)

Exact Answer

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Problem: What is 4/21 plus 2/7?
Formula / Expression: 4/21 + 2/7
Final Answer: 10/21
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Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
Notice that 21 is an exact multiple of 7 (7 × 3 = 21). The Least Common Denominator (LCD) is simply 21, meaning we only need to scale one fraction.
Working: LCD(21, 7) = 21

Step 2: Convert to Equivalent Fractions with Common Denominator 21
Multiply the numerator and denominator of 4/21 by 1, and multiply the numerator and denominator of 2/7 by 3 so both fractions share the common base 21.
Working: 4 × 1/21 × 1 = 4/21 and 2 × 3/7 × 3 = 6/21

Step 3: Add the Numerators
Now add the numerators (4 + 6 = 10) and keep the common denominator 21 unchanged.
Working: 4 + 6/21 = 10/21

Step 4: Check if the Fraction Can Be Simplified
The Greatest Common Divisor (GCD) of 10 and 21 is 1, confirming that 10/21 cannot be reduced further—it is already in its simplest irreducible form.
Working: 10/21

Step 5: Decimal & Percentage Representation
Dividing the numerator 10 by denominator 21 produces a repeating decimal (approximately 0.47619, or 47.619%).
Working: 10 ÷ 21 = 0.47619 (47.619%)

Key Values:
- Simplified Fraction: 10/21
- Mixed Number Form: 10/21
- Decimal Value: 0.47619
- Percentage: 47.619%

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Solved with FractionsCalc:
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4/21 + 2/7 = 10/21

Simplified Fraction

10/21

Mixed Number

Proper (10/21)

Decimal Value

0.47619

Percentage

47.619%

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Step-by-Step Solution: 4/21 + 2/7

Step 1

Find the Least Common Denominator (LCD)

Notice that 21 is an exact multiple of 7 (7 × 3 = 21). The Least Common Denominator (LCD) is simply 21, meaning we only need to scale one fraction.

LCD(21, 7) = 21

Step 2

Convert to Equivalent Fractions with Common Denominator 21

Multiply the numerator and denominator of 4/21 by 1, and multiply the numerator and denominator of 2/7 by 3 so both fractions share the common base 21.

4 × 1/21 × 1 = 4/21 and 2 × 3/7 × 3 = 6/21

Step 3

Add the Numerators

Now add the numerators (4 + 6 = 10) and keep the common denominator 21 unchanged.

4 + 6/21 = 10/21

Step 4

Check if the Fraction Can Be Simplified

The Greatest Common Divisor (GCD) of 10 and 21 is 1, confirming that 10/21 cannot be reduced further—it is already in its simplest irreducible form.

10/21

Step 5

Decimal & Percentage Representation

Dividing the numerator 10 by denominator 21 produces a repeating decimal (approximately 0.47619, or 47.619%).

10 ÷ 21 = 0.47619 (47.619%)

Visual Representation

The diagram below illustrates 4/21 plus 2/7 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`10/21`
Mixed Number Form	`10/21`
Decimal Form	`0.47619`
Percentage	`47.619%`

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Frequently Asked Questions

What is 4/21 plus 2/7 as a fraction?

4/21 + 2/7 in simplest fraction form is 10/21.

What is 4/21 plus 2/7 as a decimal?

4/21 + 2/7 converted to a decimal is 0.47619.

What is 4/21 plus 2/7 as a percentage?

4/21 + 2/7 expressed as a percentage is 47.619%.

Does 4/21 plus 2/7 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.47619...) because the denominator contains prime factors other than 2 and 5.