Prime Factorization and the Least Common Multiple: example 2.53

Find the LCM of $15$ and $18$ using the prime factors method.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

Find the LCM using the prime factors method. $15 and 20$

How did it go?

Write each number as a product of primes.
Write each number as a product of primes, matching primes vertically when possible.
Bring down the primes in each column.
Multiply the factors to get the LCM.	$LCM = 2 \cdot 3 \cdot 3 \cdot 5$ The LCM of 15 and 18 is 90.

Write each number as a product of primes.
Write each number as a product of primes, matching primes vertically when possible.
Bring down the primes in each column.
Multiply the factors to get the LCM.	$LCM = 2 \cdot 3 \cdot 3 \cdot 5$ The LCM of 15 and 18 is 90.