Lcm

LCM stands for Least Common Multiplier.

Start with least Prime number i.e 2, and go on; i.e 3,5,7.......

Remember the numbers must be completely divisible by the prime number, leaving no remainders.

LCM of 69, 39 will be 

69/3 = 23 ; 39/3=13

Since 23 and 13 are prime numbers there will be no other L COMMON M 

and so LCM of 69 and 39 will be 3 ;...................... 3 * (23+13) = 69+39