# One plus five is four?

First puzzle! Might be a little easy... :P

Real life has you feeling bore,

or maybe you puzzle to feel alive.

Must it all be just a chore?

A fake world is where some thrive,

no meaning in our human core.

No matter, the poetry you can ignore.

Uncover discover when one plus five,

makes the number four.

Someone I'm sure, the answer will derive.

Is it :

I + V = IV

which is

In Roman numerals, One + Five = Four.

• @humn :) It is a very easy question if someone has been playing with numbers recently... – ABcDexter Jun 12 '16 at 9:46
• There is a clue in the question about this too. If you read the first letter of each line then you get 'RoMAnNUmS' which can be read as "Roman numbers" – manshu Jun 12 '16 at 10:40
• @manshu Aah, the acrostics, love them :D – ABcDexter Jun 12 '16 at 10:41
• Glad someone noticed the clue ;) – aznbanana9 Jun 12 '16 at 15:14
• @aznbanana9 Thank you but it was only after manshu's comment here :) – ABcDexter Jun 12 '16 at 17:03

Might not be the correct answer, but you will like this:

Minus one plus five is four. Yes it is!
-1 + 5 = 4

Yet another possible answer would be

which can be viewed as addition in

a number of algebraic structures of characteristic 2, including the nimbers, the Galois fields GF(2n), and more generally any algebraic system that can be viewed as a module over the two-element ring ℤ/2ℤ of integers modulo 2,

is often written with the symbol

⊕ (a circled + sign, to distinguish it from ordinary addition),

and has the property that

1 ⊕ 5 = 0012 ⊕ 1012 = 1002 = 4.

And it even fits the rhyme!

• This didn't get the green tick, and clearly ABcDexter's solution is what the OP intended (the acrostic RoMAnNUmS spotted by manshu shows that), but still +1 for reminding us of an alternative arithmetic which has great puzzling possibilities. – Rosie F Jun 12 '16 at 16:17
• I was sure there'd be alternate solutions and included the clue for that reason, but nevertheless a great answer! – aznbanana9 Jun 12 '16 at 21:47
• Great, this answer shows a lot more effort and Mathematics involved :) – ABcDexter Jun 13 '16 at 7:35

ABcDexter's answer is probably the most 'obvious', but here's an alternative:

$5 (\text{mod } 1) + 1 (\text{mod } 1) = 4 (\text{mod } 1) = 0$

• Aah here comes the MODular arithematic, interesting :) – ABcDexter Jun 12 '16 at 9:47
• Works (mod 2) too. – Neil Jun 12 '16 at 10:35