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

  • 3
    $\begingroup$ 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. $\endgroup$ – Deusovi May 11 '16 at 3:56
  • 14
    $\begingroup$ There's 10 kinds of people in the world. Those who understand binary and those who don't. $\endgroup$ – Johannes Pille May 11 '16 at 8:09
  • 5
    $\begingroup$ @JohannesPille and those who understand Gray code. $\endgroup$ – Pierre Arlaud May 11 '16 at 8:33
  • 35
    $\begingroup$ There are 10 kinds of people - those who understand ternary, those who don't, and those who mistake it for binary! $\endgroup$ – Alexander May 11 '16 at 9:18
  • 3
    $\begingroup$ Funny thing is, I catched this instant aswell, but by catching a hint that actually wasn't one.... I read "turing" ^^ $\endgroup$ – Zaibis May 11 '16 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.

  • $\begingroup$ Oh.. Super fast ! I was typing the same :) $\endgroup$ – Arun Xavier May 11 '16 at 3:58
  • 1
    $\begingroup$ Ninja'd by the pro! $\endgroup$ – KoA May 11 '16 at 3:59
  • $\begingroup$ @ᴊᴀᴠʏ Me too, but at same time we post; after a few mins we don't :) $\endgroup$ – Jonathan Allan May 11 '16 at 4:00
  • $\begingroup$ Is the LSB usually 'last' ? I guess the hint defines it, but it took the hint... $\endgroup$ – Lamar Latrell May 11 '16 at 5:19
  • 1
    $\begingroup$ @Lamar: Yes, just like the least significant digit is last in base ten. $\endgroup$ – Deusovi May 11 '16 at 5:20

Today you are turning



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

  • $\begingroup$ Ninja'd you again. :P $\endgroup$ – Deusovi May 11 '16 at 4:00
  • $\begingroup$ @Deusovi Well you got an ^vote from me :) $\endgroup$ – Jonathan Allan May 11 '16 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


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


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


protected by Community May 11 '16 at 10:13

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