What is 4/42 plus 15/21? (Answer: 17/21)

Exact Answer

==================================================
Problem: What is 4/42 plus 15/21?
Formula / Expression: 4/42 + 15/21
Final Answer: 17/21
==================================================

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 4/42 by 1, and multiply the numerator and denominator of 15/21 by 2 so both fractions share the common base 42.
Working: 4 × 1/42 × 1 = 4/42 and 15 × 2/21 × 2 = 30/42

Step 3: Add the Numerators
Now add the numerators (4 + 30 = 34) and keep the common denominator 42 unchanged.
Working: 4 + 30/42 = 34/42

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 34 and 42, which is 2. Divide both the numerator and denominator by 2.
Working: 34 ÷ 2/42 ÷ 2 = 17/21

Step 5: Decimal & Percentage Representation
Dividing the numerator 17 by denominator 21 produces a repeating decimal (approximately 0.809524, or 80.9524%).
Working: 17 ÷ 21 = 0.809524 (80.9524%)

Key Values:
- Simplified Fraction: 17/21
- Mixed Number Form: 17/21
- Decimal Value: 0.809524
- Percentage: 80.9524%

--------------------------------------------------
Solved with FractionsCalc:
https://fractionscalc.com/what-is-4-42-plus-15-21/
==================================================

4/42 + 15/21 = 17/21

Simplified Fraction

17/21

Mixed Number

Proper (17/21)

Decimal Value

0.809524

Percentage

80.9524%

Reduce / Convert Fraction:

Convert Fraction:

Enter Decimal Number:

Enter Percentage: %

What is % of

From Value: To Value:

Simplify Ratio: :

Switch to Proportion / Missing X Solver (A/B = C/D) →

Enter 3 known numbers and leave 1 empty (or type x) to solve:

← Switch to Ratio Simplifier (A:B)

Provide any 2 values below to calculate the remaining:

Price before discount

Discount

Price after discount

You saved

+ Add Sales Tax & Extra Coupon (Optional)

Sales Tax: % Extra Off: %

Provide any 2 values below to calculate the remaining:

Cost

Markup

REVENUE

Gross Profit

Profit Margin

Bill Subtotal

Tip Percentage

Split (People)

👥

Quick Tip:

Total Bill

Split Between

👥

Tip % (Optional)

Include Tip:

Total Price

Quantity

Unit of Measure

← Discount & Sales Tax • Ratio Simplifier (A:B) →

First Number: Second Number:

Find All Factors of:

Dividend: ÷ Divisor:

Number to Round: To Nearest:

Method: Standard (5+ ↑) Always Up (Ceil) Always Down (Floor)

Presets:

√ Square Root of: OR Power (x^y): ^{^}

x² + x + = 0

Number (n! & log):

Circle Radius (r):

Side a: Side b:

Angle (Degrees): °

Numbers (comma separated):

Total Items (n): Choose (r):

Decimal Number:

Number (1–3999):

Step-by-Step Solution: 4/42 + 15/21

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 4/42 by 1, and multiply the numerator and denominator of 15/21 by 2 so both fractions share the common base 42.

4 × 1/42 × 1 = 4/42 and 15 × 2/21 × 2 = 30/42

Step 3

Add the Numerators

Now add the numerators (4 + 30 = 34) and keep the common denominator 42 unchanged.

4 + 30/42 = 34/42

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 34 and 42, which is 2. Divide both the numerator and denominator by 2.

34 ÷ 2/42 ÷ 2 = 17/21

Step 5

Decimal & Percentage Representation

Dividing the numerator 17 by denominator 21 produces a repeating decimal (approximately 0.809524, or 80.9524%).

17 ÷ 21 = 0.809524 (80.9524%)

Visual Representation

The diagram below illustrates 4/42 plus 15/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`17/21`
Mixed Number Form	`17/21`
Decimal Form	`0.809524`
Percentage	`80.9524%`

Was this solution helpful?

Help us improve our free step-by-step tools

Frequently Asked Questions

What is 4/42 plus 15/21 as a fraction?

4/42 + 15/21 in simplest fraction form is 17/21.

What is 4/42 plus 15/21 as a decimal?

4/42 + 15/21 converted to a decimal is 0.809524.

What is 4/42 plus 15/21 as a percentage?

4/42 + 15/21 expressed as a percentage is 80.9524%.

Does 4/42 plus 15/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.809524...) because the denominator contains prime factors other than 2 and 5.