Qual è il minimo comune multiplo di 9 e 15?

First we need to write out the prime factors of #9# e #15#.

#9:3xx3#
#15:3xx5#

Now we group them together:
#9:(3xx3)#
#15:(3)xx(5)#

Next we take the largest groups of each number:
#9# ha due #3#s while #15# ha 1 #5#.

We multiply the largest groups together:
#LCM(9,15)=3xx3xx5=45#

#45/15=3#, #45/9=5#