Gcd and lcm

• Find Positive Integers with GCD 10 and LCM 100
  Write each number as 10 times a coprime factor; the factor pairs of 10 give all solutions: (10, 100), (20, 50), and their reversals.
• What Is the Greatest Common Divisor of Prime Numbers?
  The gcd of two distinct primes is 1; if they are the same prime, their gcd is that prime itself.