The weight of the LSB as a binary number is:

ANS:A - 1

Lets say a number given is 5. In binary, this is 101. The LSB is the first one from right while MSB is last one from right.

The weight is simply 2^n where n is the position of the '1' from the radix pt. In 101, it is not shown but it's after the right-most 1.

The weight of LSB 1 is 2^0 =1. Weight of MSB is 2^2 = 4.