Simplify 15/21

15/21 simplified is 5/7, after dividing the top and bottom by 3.

Result

Answer

\frac{15}{21} = \textcolor{#0b5c56}{\frac{5}{7}}

15/21 simplifies to 5/7.

  • Greatest common factor: 3
  • Decimal: \displaystyle 0.\overline{714285} (the 714285 repeats forever, about 0.7143)
  • Percent: 71.43%
15/215/7

Same amount, fewer parts

Step-by-step solution

The problem

\frac{15}{21}

  1. Find the greatest common factor. List the factors of each:
    Factors of 15: 1, 3, 5, 15
    Factors of 21: 1, 3, 7, 21
    The greatest common factor (GCF) is 3.

    \text{GCF}(15, 21) = 3

  2. Divide the top and bottom by 3. Dividing both by the same number keeps the value the same.

    = \frac{15 \div 3}{21 \div 3} = \textcolor{#0b5c56}{\frac{5}{7}}

All the working together

\begin{aligned} &\frac{15}{21} \\[8pt] &= \frac{15 \div 3}{21 \div 3} && \textcolor{#5b6660}{\textsf{divide by 3}} \\[8pt] &= \textcolor{#0b5c56}{\frac{5}{7}}\end{aligned}

15/21 in other forms

Simplest form5/7
Greatest common factor3
Decimal0.714285… (the 714285 repeats forever)
Percent≈ 71.43%
Equal fractions10/14, 20/28, 25/35, 30/42

Fractions over 21 simplified

FractionSimplest formDecimal
1/21already simplest0.047619…
2/21already simplest0.095238…
3/211/70.142857…
4/21already simplest0.190476…
5/21already simplest0.238095…
6/212/70.285714…
7/211/30.333…
8/21already simplest0.380952…
9/213/70.428571…
10/21already simplest0.476190…
11/21already simplest0.523809…
12/214/70.571428…
13/21already simplest0.619047…
14/212/30.666…
15/215/70.714285…
16/21already simplest0.761904…
17/21already simplest0.809523…
18/216/70.857142…
19/21already simplest0.904761…
20/21already simplest0.952380…

Frequently asked questions

What is 15/21 in simplest form?

15/21 simplifies to 5/7. Divide the top and bottom by 3, their greatest common factor: 15 ÷ 3 = 5 and 21 ÷ 3 = 7.

What is the greatest common factor of 15 and 21?

The GCF of 15 and 21 is 3 – the biggest number that divides both with nothing left over.

Is 15/21 equal to 5/7?

Yes. Both are 0.714285… (≈ 71.43%). Simplifying changes how the fraction is written, not its value.

More fractions to simplify

Any other fraction or mixed number: use the Simplify Fractions Calculator.