2 x 3 x 3 x 5 = 90
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The numbers are relatively prime, or co-prime.
30 is the product of three different prime numbers.
If the GCF of a given pair of numbers is 1, the LCM will be equal to their product. If the GCF is greater than 1, the LCM will be less than their product. Or, stated another way, if the two numbers have no common prime factors, their LCM will be their product.
Yes, it is always. Assume temporarily that the product of two prime numbers is not always composite. This implies that that at least one product of prime numbers is also prime. Now, say two different prime numbers p and q, when multiplied, equal r. If r is a prime number, then r's only positive factors are 1 and r. But 1 is not a prime number. This contradicts that both p and q are prime (because either p or q MUST be 1). Therefore, the product of two prime numbers is always composite.
Any two that are relatively prime.