What is 18/38 plus 11/21? (Answer: 398/399)

Exact Answer

==================================================
Problem: What is 18/38 plus 11/21?
Formula / Expression: 18/38 + 11/21
Final Answer: 398/399
==================================================

Step-by-Step Solution:

Step 1: Find the Least Common Denominator (LCD)
The denominators 38 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 38 × 21 = 798.
Working: LCD(38, 21) = 798

Step 2: Convert to Equivalent Fractions with Common Denominator 798
Multiply the numerator and denominator of 18/38 by 21, and multiply the numerator and denominator of 11/21 by 38 so both fractions share the common base 798.
Working: 18 × 21/38 × 21 = 378/798 and 11 × 38/21 × 38 = 418/798

Step 3: Add the Numerators
Now add the numerators (378 + 418 = 796) and keep the common denominator 798 unchanged.
Working: 378 + 418/798 = 796/798

Step 4: Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 796 and 798, which is 2. Divide both the numerator and denominator by 2.
Working: 796 ÷ 2/798 ÷ 2 = 398/399

Step 5: Decimal & Percentage Representation
Dividing the numerator 398 by denominator 399 produces a repeating decimal (approximately 0.997494, or 99.7494%).
Working: 398 ÷ 399 = 0.997494 (99.7494%)

Key Values:
- Simplified Fraction: 398/399
- Mixed Number Form: 398/399
- Decimal Value: 0.997494
- Percentage: 99.7494%

--------------------------------------------------
Solved with FractionsCalc:
https://fractionscalc.com/what-is-18-38-plus-11-21/
==================================================

18/38 + 11/21 = 398/399

Simplified Fraction

398/399

Mixed Number

Proper (398/399)

Decimal Value

0.997494

Percentage

99.7494%

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: 18/38 + 11/21

Step 1

Find the Least Common Denominator (LCD)

The denominators 38 and 21 are coprime (they share no common factors other than 1). Therefore, their Least Common Denominator (LCD) is simply their direct product: 38 × 21 = 798.

LCD(38, 21) = 798

Step 2

Convert to Equivalent Fractions with Common Denominator 798

Multiply the numerator and denominator of 18/38 by 21, and multiply the numerator and denominator of 11/21 by 38 so both fractions share the common base 798.

18 × 21/38 × 21 = 378/798 and 11 × 38/21 × 38 = 418/798

Step 3

Add the Numerators

Now add the numerators (378 + 418 = 796) and keep the common denominator 798 unchanged.

378 + 418/798 = 796/798

Step 4

Simplify the Fraction to Lowest Terms

Find the Greatest Common Divisor (GCD) of 796 and 798, which is 2. Divide both the numerator and denominator by 2.

796 ÷ 2/798 ÷ 2 = 398/399

Step 5

Decimal & Percentage Representation

Dividing the numerator 398 by denominator 399 produces a repeating decimal (approximately 0.997494, or 99.7494%).

398 ÷ 399 = 0.997494 (99.7494%)

Visual Representation

The diagram below illustrates 18/38 plus 11/21 visually:

Summary & Alternative Representations

Property / Format	Value
Lowest Terms Fraction	`398/399`
Mixed Number Form	`398/399`
Decimal Form	`0.997494`
Percentage	`99.7494%`

Was this solution helpful?

Help us improve our free step-by-step tools

Frequently Asked Questions

What is 18/38 plus 11/21 as a fraction?

18/38 + 11/21 in simplest fraction form is 398/399.

What is 18/38 plus 11/21 as a decimal?

18/38 + 11/21 converted to a decimal is 0.997494.

What is 18/38 plus 11/21 as a percentage?

18/38 + 11/21 expressed as a percentage is 99.7494%.

Does 18/38 plus 11/21 result in a terminating or repeating decimal?

It results in a repeating decimal (approximately 0.997494...) because the denominator contains prime factors other than 2 and 5.