So my son is starting to show an interest in mathematics, and being the awesome dad that I am, I decided to buy him a basic calculator. Being the cheapskate that I am, I ordered the cheapest one I could find, which happened to be from NoSlaves™ Calculator Co. (When only the cheapest calculator will do, make sure you buy from NoSlaves™, where we lovingly craft our calculators to almost adequate levels of quality, and totally don't use any slave labour... at all.)
Unfortunately (and surprisingly), when it arrived, there seemed to be something wrong with it... I plugged in a few quick test calculations:
1 + 1 = 1 4 + 3 = 9 8 - 3 + 5 = 6 24 + 51 = 84 50 - 74 + 39 = 98
Now, I like to complain as much as the next guy, so I went hunting through the instruction manual for the company's phone number. However, on the warranty and support information page, I found the following, scrawled in a strange, dark reddish, congealed ink of some sort:
2 - 3 + 4 = ?
80 - 17 = ?
4 - 1 + 2 - _ = ?
Curious, I entered in the calculations... I didn't know what the underscore meant, so just ignored it, but regardless, the results were even more broken than my initial test calculations. By this stage I was bored, so I shrugged it off and went to bed.
Three weeks later, being the brilliant detective I am, I suddenly realised that the hand written message carried a cleverly concealed secret message. I immediately phoned the police department and was hailed as a hero.
What was wrong with the calculator? And, what was the mysterious hidden message?