We also say that

*a*and*b*are**congruent modulo**if they have the same remainder after division by*n**n*.### Examples

- The numbers 9 and 21 are congruent modulo 12, as we can see in the notation system for hours
*modulo 12*, 21 hours corresponds to 9 o’clock at night. - The numbers 25 and 45 are congruent modulo 10 because their difference, which is 45 – 25 = 20, is a multiple of 10.