# It’s the Friday Puzzle!

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Please do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

I have a cage in my garden and it contains only chickens and rabbits (I don’t really, but play along). There are 72 heads and 200 feet in the cage. How many chickens are there, and how many rabbits?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

## 70 comments on “It’s the Friday Puzzle!”

1. eivindvs says:

2 minutes, using pencil and paper.

• Eddie says:

2 minutes using a Pilot Hi Techpoint V-2000* and paper.

• jh says:

Same here, but with a Uni-ball Signo 207. I prefer retractables to pens with caps 😉

• Goliath says:

Another 2 minutes on lined paper and a V-Pen fountain pen from Pilot.

• jh says:

I just tried with a half-eaten blunt-ish Ikea pencil and was stunned to see that I reached the same solution!

• Hugh Janus says:

I recall reading a similar problem with foxes and chickens in a cage. Less successful ….

• Slange Navarr says:

One of the funniest things I’ve ever read, Janus. Well done. My rectum all but prolapsed because I was laughing so hard. You’re a comedy genius.

2. Michelle says:

Took 1 minute, really easy this week

• Hugh Janus says:

60 seconds with a green crayon. They don’t allow any sharp, pointed items here …..

• Slange Navarr says:

Another *belting* one-liner, Janus. I don’t know how you manage them so consistently, week after week. Your comedy is a gift to us all.

• Eddie says:

Goliath, any self respecting numbers man (or woman) uses squared note paper not lined paper. How else are you going to draw matrices and invert them, as required for this puzzle?

3. Anonymous says:

5 minutes and 5 tries- me not smat

4. Math Genius says:

44 chickens and 28 rabbits.

• Anonymussel says:

You might be a math genius but you’re not a reading genius, are you?

Window licker.

• ian says:

“Math genius”.

Not so much at reading though ;).

• ian says:

Arrgh – too slow!

• Bryan Atherton says:

You really do spoil it for everyone don’t you?
I had the result after two guesses and 2/3 minutes

• Anonymous says:

Too slow if you’re just being a spoiler or no genius at all.

• Andrew says:

For those who have had their enjoyment spoiled (I got it in a couple of minutes, but the way):
Add the symbol for Time to the unit for Power, followed by the unit for electrical Current and finish with more Time. The result describes Math Genius

• Anne Elk says:

Andrew: I couldn’t agree more! Thanks for making me smile. 🙂

• One Eyed Jack says:

Congratulations, Math Genius. You solved a middle school algebra problem. Check your mail. I’m sure they’re shipping the Fields Medal as I write this.

5. VicinCA says:

1.5 min, using simultaneous equations. I’m glad I don’t look at the comments before I try to solve the puzzle. Somebody always has to ruin it by not following directions.

6. Skatz says:

Phew. Trial and error in my head it took about 5 mins. There must be a formula for this to make it quicker, can someone post it on Monday please?

• ChrisR says:

It’s called ‘simultaneous equations’ – yes, come back on Monday and I’m sure someone will help. Oh, by the way there are 2 more rabbits now 🙂

7. ChrisR says:

20 seconds for an answer then another 20 to check.it is correct.
Then 20 seconds more to read the comments and see what other people think and to get further confirmation that I’d got it right (sigh!)

• Anonymous says:

You really needed confirmation? Was that because it seemed too easy?

• ChrisR says:

I wasn’t looking for confirmation here, just for the insightful and witty comments – the confirmation found me

8. I’m glad the puzzle stopped there. I was dreading the appearance of grain, wolves and a river.

• Dr Bob says:

Here’s a better answer to the problem about a wolf and a river that you were never taught –
http://xkcd.com/1134/

9. Fran6co says:

That’s not “parallel thinking”… just a mere maths problem… and very common too.

10. Roland says:

It would be a real puzzle if Richard had asked, how many 3-legged rabbits are in his cage 😉

• ChrisR says:

It’s the three-legged chickens that are the nuisance – great for drumsticks but really difficult to catch

11. Bob M says:

2.5 minutes, paper and a lamy safari fountain pen.

12. Pitmonster says:

30 secs to do the logic in my head, and then the same to check the sums in Excel.

In fairness this was not a new puzzle to me

13. Moray says:

I live for the simultaneous equations puzzles!

14. Stan says:

I had to cheat and do it using algebra (simultaneous eqs). But I’m most interested in how people did it in their heads, and quickly.

• Duncan says:

That’s not cheating and I the only other way I can think of doing it is trial and error. The arithmetic is easy enough that some people will be able to do it in their heads.

15. SofARMaths says:

1 min. Algebreasy

16. mittfh says:

I quickly worked out the separate equations for heads and legs, but couldn’t reconcile them down to a single unknown variable (hey, it’s been years since I last did any decent algebra!), so cheated with Excel (one column for rabbits, one column for chickens, another column to calculate heads; look down and find the numbers that correspond to 200 heads).

• Eddie says:

The Gordian knot approach…

17. Anonymous says:

got

18. Darek Olak says:

2 seconds concept and 10 seconds math.

19. @Sceptic_Tank says:

About 30secs in my head, then around the same double-checking on paper. I am not sure whether my mental maths was based on simultaneous equations – it’s too many years ago to remember how they work!

• Duncan says:

Come back and tell us on Monday how you did it. You could be using simultaneous eq’s without realising. I’d like to see any other ways of solving this.

20. Jim says:

One minute to find a piece of paper and a pencil without a broken lead. One more minute to solve it. Simultaneous Solutions

Aren’t rabbit’s feet meant to be lucky?

22. Stewart says:

3 minutes including 2 minutes looking for my lucky rabbit’s foot.

23. My daughter, who is a veterinarian, claims that penned chickens will murder interlopers of a different species. So, do you want to check those numbers again, Richard?

24. pete says:

Any 3 legged wabbits?

25. NickC says:

26. bletherskite says:

Glad I actually worked out the answer myself before flamin Maths Genius decided to ignore the request and provide spoilers! Took me about 5 mins.

• Anonymous says:

Did it on the toilet nothing to write with. Is it wrong to consult twitter whilst attending an evacuation? I’d say yes but I can’t be alone and the mental exercise helps.

27. ivan says:

Barely even 10 seconds. Surely pen and paper and simultaneous equations is overkill for a baby problem like this.

28. Jaleel Hamid says:

got it!

29. Fotoflex says:

It took me a few minutes, starting with 50/50, and working towards the solution.
By which time there were twice as many rabbits.

30. Fifty years.

31. auntiejulie says:

What did the fox say?

32. Lazy T says:

If there are only chicks and bunnies in the cage – 2min,
if any creepie-crawlies were in there too then I failed.
Pencil stub and gas bill envelope.

33. Diane says:

About a minute, on the backside of what I was supposed to be working on. And they said I’d never use algebra in real life.

34. carlo says:

30 seconds, with no pen, using an easy strategy: I’ll post it on monday 🙂

35. Kenny P says:

Wow this is really puzzling to be honest. It’s funny how I looked at it and analyzed and think I’d be simple as hell to figure out.

36. James Bailey says:

Took about two or three minutes, mostly in my head, via a process of elimination (no animals were harmed in said process). Been too long since I’ve worked out anything like this using any sort of formula that I wouldn’t remember the procedure.

37. Bobby says:

This is the classical chinese puzzle.

38. 30 seconds, no pen paper nor spreadsheet

39. The puzzle was a doddle but what I don’t understand is the need for spreadsheets, simultaneous equations, guesswork or even pens/pencils – it’s simple arithmetic that can be done in the head in just a couple of seconds! (Or maybe I’m the real “Maths Genius” since I can read as well 🙂 )

40. zippy says:

It took a minute to go through mentally. There’s a really simple shortcut which does away with the need for equations and pens and paper.

41. Anonymous says:

The good answer was : one (… but only in Tchernobyl)

42. Bill says:

Found it!! Classic problem! 😉

43. Ronda says:

Hmph. This took me a good 7-8 minutes, mostly because I couldn’t figure out the right algebraic equation. I thought it was going to be totally easy, but the first equation I came up with was gobbledygook.

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