What is 15/54 plus 8/21? (Answer: 83/126)

Exact Answer

==================================================
Problem: What is 15/54 plus 8/21?
Formula / Expression: 15/54 + 8/21
Final Answer: 83/126
==================================================

Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 54 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 378 (which is smaller than their product 54 × 21 = 1134, keeping the calculation simpler).
Working: LCD(54, 21) = 378

Step 2: Convert to Equivalent Fractions with Common Denominator 378
Multiply the numerator and denominator of 15/54 by 7, and multiply the numerator and denominator of 8/21 by 18 so both fractions share the common base 378.
Working: 15 × 7/54 × 7 = 105/378 and 8 × 18/21 × 18 = 144/378

Step 3: Add the Numerators
Now add the numerators (105 + 144 = 249) and keep the common denominator 378 unchanged.
Working: 105 + 144/378 = 249/378

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 249 and 378, which is 3. Divide both the numerator and denominator by 3.
Working: 249 ÷ 3/378 ÷ 3 = 83/126

Step 5: Decimal & Percentage Representation
Dividing the numerator 83 by denominator 126 produces a repeating decimal (approximately 0.65873, or 65.873%).
Working: 83 ÷ 126 = 0.65873 (65.873%)

Key Values:
- Simplified Fraction: 83/126
- Mixed Number Form: 83/126
- Decimal Value: 0.65873
- Percentage: 65.873%

--------------------------------------------------
Solved with FractionsCalc:
https://fractionscalc.com/what-is-15-54-plus-8-21/
==================================================

15/54 + 8/21 = 83/126

Simplified Fraction

83/126

Mixed Number

Proper (83/126)

Decimal Value

0.65873

Percentage

65.873%

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: 15/54 + 8/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 54 and 21 share a common factor (GCD = 3). Finding their Least Common Multiple gives an LCD of 378 (which is smaller than their product 54 × 21 = 1134, keeping the calculation simpler).

LCD(54, 21) = 378

Step 2

Convert to Equivalent Fractions with Common Denominator 378

Multiply the numerator and denominator of 15/54 by 7, and multiply the numerator and denominator of 8/21 by 18 so both fractions share the common base 378.

15 × 7/54 × 7 = 105/378 and 8 × 18/21 × 18 = 144/378

Step 3

Add the Numerators

Now add the numerators (105 + 144 = 249) and keep the common denominator 378 unchanged.

105 + 144/378 = 249/378

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 249 and 378, which is 3. Divide both the numerator and denominator by 3.

249 ÷ 3/378 ÷ 3 = 83/126

Step 5

Decimal & Percentage Representation

Dividing the numerator 83 by denominator 126 produces a repeating decimal (approximately 0.65873, or 65.873%).

83 ÷ 126 = 0.65873 (65.873%)

Visual Representation

The diagram below illustrates 15/54 plus 8/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`83/126`
Mixed Number Form	`83/126`
Decimal Form	`0.65873`
Percentage	`65.873%`

Was this solution helpful?

Help us improve our free step-by-step tools

Frequently Asked Questions

What is 15/54 plus 8/21 as a fraction?

15/54 + 8/21 in simplest fraction form is 83/126.

What is 15/54 plus 8/21 as a decimal?

15/54 + 8/21 converted to a decimal is 0.65873.

What is 15/54 plus 8/21 as a percentage?

15/54 + 8/21 expressed as a percentage is 65.873%.

Does 15/54 plus 8/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.65873...) because the denominator contains prime factors other than 2 and 5.