What is the Lcm of 5/8?

Write the multiple of 5 and 8

5 = 5, 10, 15, 20, 25, 30, 35, 40,.....

8 = 8, 16, 24, 32, 40, 48, 53,.....

We can observe that 40 is least common multiple in both. So LCM is 40

All you have to do is list the multiplies of both of the numbers and look for the common number.  (as Deepak has demonstrated)