3 + 2 = 1

When is the equation

3 + 2 = 1

true?


There are some situations where it is true.


Trust me, it's true under certain circumstances.


Need a hint?


Okay.


Think about a clock.


Doesn't help?


Think of the face of a clock, and then think of what the answer to this equation might be:


10 + 3 = ?


If you start at ten o'clock, and add three hours, do you end up at thirteen o'clock?


No, you end up at one o'clock.


10 + 3 = 1


This is true when the modulus is 12.


The modulus is any number which reverts back to zero during a mathematical operation. You use only the numbers that fall between zero and the modulus. In the case of clock math, you only use 1 through 12. (In the case of clock math, 0 is read as 12.) So, in clock math,


Adding ten hours to eight o'clock yields


8 + 10 = (18 - 12) = 6


Or, if Suzie has three two-hour classes starting at 9 am, when does she get out of class?


9 + (3 x 2) = 9 + 6 = (15 - 12) = 3


Now, back to the original question.


When does 3 + 2 = 1?


Well, normally, 3 + 2 = 5 ...


Unless the modulus is 4.


Then, 3 + 2 = (5 - 4) = 1


There! Now, file that away in your brain for the next time you want to stump a mathematically inclined friend.