Thus to find a+mb, we add a and b in the ordinary way and then from the sum, we remove integral multiples of m in such a way that the remainder r is either 0 or a positive integer less than m. When a and b are two integers such that a–b is divisible by a fixed positive integer m, then we have a≡b(modm).

What is addition mod n?

For any positive integer n, let S be the complete set of residues {0, 1, 2,…, n−1}. Then addition modulo n on S is defined as follows. For a and b in S, take the usual sum of a and b as integers, and let r be the element of S to which the result is congruent (modulo n); the sum a+b (mod n) is equal to r.

How do you find the solution of a mod?

To solve a linear congruence ax ≡ b (mod N), you can multiply by the inverse of a if gcd(a,N) = 1; otherwise, more care is needed, and there will either be no solutions or several (exactly gcd(a,N) total) solutions for x mod N.