What is 15/28 plus 15/21?
15/28 plus 15/21 equals 5/4 (or 1 1/4 as a mixed number) (or 1.25 in decimal form). Learn the step-by-step solution to add 15/28 and 15/21 using Least Common Denominator and simplification.
Exact Answer
15/28 + 15/21 = 5/4
Simplified Fraction
5/4
Mixed Number
1 1/4
Decimal Value
1.25
Percentage
125%
Step-by-Step Solution: 15/28 + 15/21
Step 1
Find the Least Common Denominator (LCD)
The denominators 28 and 21 share a common factor (GCD = 7). Finding their Least Common Multiple gives an LCD of 84 (which is smaller than their product 28 × 21 = 588, keeping the calculation simpler).
LCD(28, 21) = 84
Step 2
Convert to Equivalent Fractions with Common Denominator 84
Multiply the numerator and denominator of 15/28 by 3, and multiply the numerator and denominator of 15/21 by 4 so both fractions share the common base 84.
15 × 3/28 × 3 = 45/84 and 15 × 4/21 × 4 = 60/84
Step 3
Add the Numerators
Now add the numerators (45 + 60 = 105) and keep the common denominator 84 unchanged.
45 + 60/84 = 105/84
Step 4
Simplify the Fraction to Lowest Terms
Find the Greatest Common Divisor (GCD) of 105 and 84, which is 21. Divide both the numerator and denominator by 21.
105 ÷ 21/84 ÷ 21 = 5/4
Step 5
Convert Improper Fraction to a Mixed Number
Since the numerator (5) is greater than the denominator (4), divide 5 by 4: it goes in 1 whole time(s) with a remainder of 1, giving the mixed number 1 1/4.
5/4 = 11/4
Step 6
Decimal & Percentage Representation
Dividing the numerator 5 by denominator 4 yields an exact terminating decimal of 1.25 (or 125%).
5 ÷ 4 = 1.25 (125%)
Visual Representation
The diagram below illustrates 15/28 plus 15/21 visually:
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Summary & Alternative Representations
| Property / Format | Value |
|---|---|
| Lowest Terms Fraction | 5/4 |
| Mixed Number Form | 1 1/4 |
| Decimal Form | 1.25 |
| Percentage | 125% |
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Frequently Asked Questions
What is 15/28 plus 15/21 as a fraction?
15/28 + 15/21 in simplest fraction form is 5/4 (or 1 1/4 as a mixed number).
What is 15/28 plus 15/21 as a decimal?
15/28 + 15/21 converted to a decimal is 1.25.
What is 15/28 plus 15/21 as a percentage?
15/28 + 15/21 expressed as a percentage is 125%.
How do you write 15/28 plus 15/21 as a mixed number?
Because the numerator is greater than the denominator, the improper fraction 5/4 can be written as the mixed number 1 1/4.
Does 15/28 plus 15/21 result in a terminating or repeating decimal?
It results in an exact terminating decimal (1.25) because the denominator in simplest terms contains only prime factors 2 and/or 5.