For any integer n and where k is power of 2,

n % k = n & (k-1)

Example : Let n = 26 and k = 2 ^ 3 = 8 , so 26 % 8 = 2
bin(26)  = 11010
bin(8-1) = 00111
26 & 7   = 00010 = 2, which is CORRECT

I wasn't able to proof this statement, how could it be proofed without taking number as example?

Thanks in Advance!