Pre-Algebra Examples

$5 x^{3} y$ , $15 x y$

Step 1

Since $5 x^{3} y, 15 x y$ contains both numbers and variables, there are two steps to find the LCM. Find LCM for the numeric part $5, 15$ then find LCM for the variable part $x^{3}, y^{1}, x^{1}, y^{1}$ .

Step 2

The LCM is the smallest positive number that all of the numbers divide into evenly.

1. List the prime factors of each number.

2. Multiply each factor the greatest number of times it occurs in either number.

Step 3

Since $5$ has no factors besides $1$ and $5$ .

$5$ is a prime number

Step 4

$15$ has factors of $3$ and $5$ .

$3 \cdot 5$

Step 5

Multiply $3$ by $5$ .

$15$

Step 6

The factors for $x^{3}$ are $x \cdot x \cdot x$ , which is $x$ multiplied by each other $3$ times.

$x^{3} = x \cdot x \cdot x$

$x$ occurs $3$ times.

Step 7

The factor for $y^{1}$ is $y$ itself.

$y^{1} = y$

$y$ occurs $1$ time.

Step 8

The factor for $x^{1}$ is $x$ itself.

$x^{1} = x$

$x$ occurs $1$ time.

Step 9

The factor for $y^{1}$ is $y$ itself.

$y^{1} = y$

$y$ occurs $1$ time.

Step 10

The LCM of $x^{3}, y^{1}, x^{1}, y^{1}$ is the result of multiplying all prime factors the greatest number of times they occur in either term.

$x \cdot x \cdot x \cdot y$

Step 11

Simplify $x \cdot x \cdot x \cdot y$ .

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Step 11.1

Multiply $x$ by $x$ .

$x^{2} \cdot x \cdot y$

Step 11.2

Multiply $x^{2}$ by $x$ by adding the exponents.

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Step 11.2.1

Multiply $x^{2}$ by $x$ .

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Step 11.2.1.1

Raise $x$ to the power of $1$ .

$x^{2} \cdot x^{1} \cdot y$

Step 11.2.1.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$x^{2 + 1} \cdot y$

Step 11.2.2

Add $2$ and $1$ .

$x^{3} \cdot y$

$x^{3} y$

Step 12

The LCM for $5 x^{3} y, 15 x y$ is the numeric part $15$ multiplied by the variable part.

$15 x^{3} y$