# It's my birthday today - how old am I turning?

It is my birthday today
Last year I had 5 candles
4 were lit the last was not
But today, I'll light them all

How old am I turning today?

HINT: I am not turning 5 today and...

Next year I'll have 6 candles, but I'll only light the first

• Hey, welcome to Puzzling! This is a good first puzzle but I highly recommend holding off on giving hints - often you'll find out you don't need them.
– Deusovi
Commented May 11, 2016 at 3:56
• There's 10 kinds of people in the world. Those who understand binary and those who don't. Commented May 11, 2016 at 8:09
• @JohannesPille and those who understand Gray code. Commented May 11, 2016 at 8:33
• There are 10 kinds of people - those who understand ternary, those who don't, and those who mistake it for binary! Commented May 11, 2016 at 9:18
• Funny thing is, I catched this instant aswell, but by catching a hint that actually wasn't one.... I read "turing" ^^ Commented May 11, 2016 at 15:15

You're turning

11111 (Or 31)! This is because you light your candles in binary: last year you turned 30 (11110) so you only lit the first four candles.

• Oh.. Super fast ! I was typing the same :) Commented May 11, 2016 at 3:58
• Ninja'd by the pro!
– KoA
Commented May 11, 2016 at 3:59
• @ᴊᴀᴠʏ Me too, but at same time we post; after a few mins we don't :) Commented May 11, 2016 at 4:00
• Is the LSB usually 'last' ? I guess the hint defines it, but it took the hint... Commented May 11, 2016 at 5:19
• @Lamar: Yes, just like the least significant digit is last in base ten.
– Deusovi
Commented May 11, 2016 at 5:20

Today you are turning

31

Since

you are lighting your candles in binary, $11110 = 30; 11111 = 31; 100000 = 32$

• Ninja'd you again. :P
– Deusovi
Commented May 11, 2016 at 4:00
• @Deusovi Well you got an ^vote from me :) Commented May 11, 2016 at 4:01

I've got a different solution, that is very close to the current one, but a little bit different. (and fits of course)

He is turning

30. Every candle that is lit stands for 6 years. Every candle that is not lit stands for 5 years. (5 candles lit is 5x6=30) And next year he becomes 31 (1 candle lit, 5 not. 1x6+5x5=31)

You're turning

31

Since the analogy is in

binary and the candles represent face values of the numbers,

you light the first 4

Next year you'll turn

32

and only light the first candle and not the other 5.