Pre-Algebra Examples

$30 a b^{3}$ , $20 a b^{3}$

Step 1

Since $30 a b^{3}, 20 a b^{3}$ contains both numbers and variables, there are two steps to find the LCM. Find LCM for the numeric part $30, 20$ then find LCM for the variable part $a^{1}, b^{3}, a^{1}, b^{3}$ .

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

The prime factors for $30$ are $2 \cdot 3 \cdot 5$ .

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Step 3.1

$30$ has factors of $2$ and $15$ .

$2 \cdot 15$

Step 3.2

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

$2 \cdot 3 \cdot 5$

Step 4

The prime factors for $20$ are $2 \cdot 2 \cdot 5$ .

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Step 4.1

$20$ has factors of $2$ and $10$ .

$2 \cdot 10$

Step 4.2

$10$ has factors of $2$ and $5$ .

$2 \cdot 2 \cdot 5$

Step 5

The LCM of $30, 20$ is the result of multiplying all prime factors the greatest number of times they occur in either number.

$2 \cdot 2 \cdot 3 \cdot 5$

Step 6

Multiply $2 \cdot 2 \cdot 3 \cdot 5$ .

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Step 6.1

Multiply $2$ by $2$ .

$4 \cdot 3 \cdot 5$

Step 6.2

Multiply $4$ by $3$ .

$12 \cdot 5$

Step 6.3

Multiply $12$ by $5$ .

$60$

Step 7

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

$a^{1} = a$

$a$ occurs $1$ time.

Step 8

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

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

$b$ occurs $3$ times.

Step 9

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

$a^{1} = a$

$a$ occurs $1$ time.

Step 10

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

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

$b$ occurs $3$ times.

Step 11

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

$a \cdot b \cdot b \cdot b$

Step 12

Simplify $a \cdot b \cdot b \cdot b$ .

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Step 12.1

Multiply $b$ by $b$ by adding the exponents.

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Step 12.1.1

Move $b$ .

$a \cdot (b \cdot b) \cdot b$

Step 12.1.2

Multiply $b$ by $b$ .

$a \cdot b^{2} \cdot b$

Step 12.2

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

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Step 12.2.1

Move $b$ .

$a \cdot (b \cdot b^{2})$

Step 12.2.2

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

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Step 12.2.2.1

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

$a \cdot (b^{1} b^{2})$

Step 12.2.2.2

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

$a \cdot b^{1 + 2}$

Step 12.2.3

Add $1$ and $2$ .

$a \cdot b^{3}$

$a b^{3}$

Step 13

The LCM for $30 a b^{3}, 20 a b^{3}$ is the numeric part $60$ multiplied by the variable part.

$60 a b^{3}$