#27. Sounds like funny bone. (7)

]]>Well, I just finished solving the puzzle again for a final check...and all is ok.

But - and wouldn't you know it! - of course I spotted a further improvement opportunity and have edited the puzzle again. The change mainly affects the class-number component and increases the difficulty level of its solution, but at the same time it fixes a clue that was a bit unsatisfactory but for which I hadn't been able to find a better alternative until now.

Latest revision:

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Yes, the given solution method is rather starter-ish.

However, it is possible to construct a nice mathematical formula in terms of *n* that eliminates all that counting, and which, for *n*=12, will immediately give you the answer for 12 days.

Hints:

1. The number of presents given daily over the 12 days forms a well-known series, about which there are help pages here on MIF.

2. Further information about summing the terms of the series can be found on the net.

This puzzle is also discussed here.

]]>Pick any 4-digit number at all (should not have the same digit throughout). Rearrange the digits to form as many 4-digit numbers as possible. From the range of numbers (including the one you first picked), subtract the least from the greatest. If the difference is a 2-digit number add the digits together.

The idea behind this is no matter what your answer will always be 9. Yes try it now.

Okay.

1234

1234 1243 1324 1342 1423 1432

2134 2143 2314 2341 2413 2431

3124 3142 3214 3241 3412 3421

4123 4132 4213 4231 4312 4321

4321

1234

----

3087

Well, it's 4 digits but I'll go add it... 3+0+8+7 = 18 (1 + 8) = **9**.

Worth that 10 minute typing. BTW, the name of the topic reminds me of a book I borrow in the library at my school.

]]>1. Rh1 Rf8

2. Rh3 Rd8

3. Rh1 Rf8

4. Rh3 Rd8

.

.

Black would be very pleased indeed if White went 5. Rh1!

Agnishom wrote:

There are also many ways to iterate the game infinitely

'Infinitely' is not possible these days under FIDE Laws of Chess.

]]>Oz seems really interresting.

]]>When you start the fire in the middle why does it spread westward against the wind direction? This puzzle has come up before and I gave an alternative solution in post 6 of

http://www.mathisfunforum.com/viewtopic.php?id=20864

Bob

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