Perform the addition on the 12-hour clock 5 plus 11?

Answer 1

This is know as addition mod 12 or clock addition. 5 plus 11 usually equals 16 but there is no 16 on a 12 hour clock. The biggest number is 12 so 16-12 is 4 and the answer is 4. Of course you do not need the above explanation to see this. Think of starting at 5 and adding 12 hours. That would of course bring you back to 5. Now if you add one less then it is 4. So we can add 11 or subtract 1 from 5. This is because 11 is congruent to -1 mod 12. If a is congruent to b mod 12 this simply means a-b is a multiple of 12 . Now 11- (-1) is 12 which is 12x1 so it is a multiple of 12.