Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

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#56026 Re: Puzzles and Games » Chess Puzzles » 2009-04-20 00:00:42

Hi ganesh;

I won't hide the answer because no one is checking this topic anymore.

Answer to 33:

  Generally an expert player (rating around 2000) could easily force mate from that position in under 50 moves. A grandmaster (rating about 2500 - 2600) could force mate in that position in under 35 moves. Most computer chess engines can do it in around 30 moves.

#56027 Re: Puzzles and Games » Connotations. » 2009-04-19 21:12:08

1 count

2 pleasant

3 coherent

#56028 Re: Formulas » Logarithm Formulas » 2009-04-19 19:39:47

Hi random_fruit;

It could be a quiz problem and I agree it appears  to have only 1 solution in R.

#56031 Re: Puzzles and Games » Puzzlers - you can use the "Hide" tag » 2009-04-19 18:13:56

Hi quittyqat;

  I did click it. It says "Highlight this message." Is that what is supposed to happen?

#56032 Re: Puzzles and Games » Connotations. » 2009-04-19 13:15:45

1 mean

2 delectable

3 incision

#56033 Re: Exercises » Challenge of the Day: » 2009-04-19 07:45:08

Hi ganesh;

Here is my answer to #10

Now multiply numerator and denominator by

#56034 Re: Puzzles and Games » Puzzlers - you can use the "Hide" tag » 2009-04-19 05:45:39

OK. quittyqat now you got me, I just see an empty box. Was that on purpose? Art is even more difficult for me than math or chess.

bobbym

#56035 Re: Help Me ! » Percentages » 2009-04-19 05:39:51

Hi suresh1969

   Thats because I am a simpleton. Just ask anybody for confirmation of that fact. You really find out how much you know about something when you try to explain it in simple terms. Its the hardest thing in the world to do. I remember a story about David Hilbert along those lines.

I really do think that identity's post to you
http://www.mathisfunforum.com/viewtopic.php?id=11996
is really a good example of a simple and lucid answer.

bobbym

#56036 Re: Guestbook » math » 2009-04-18 18:10:40

Hi quittyqat;

I got this one!

My answer

bobbym

#56038 Re: Exercises » Challenge of the Day: » 2009-04-18 17:22:12

Hi ganesh;

The answer to #4 is (3) 555681

#56039 Re: Puzzles and Games » Puzzlers - you can use the "Hide" tag » 2009-04-18 16:04:48

Hi quittyqat;

  The one you picked looks best but maybe only to me.

bobbym

#56040 Re: Dark Discussions at Cafe Infinity » using calculators as proof » 2009-04-18 04:02:03

Hi Mikau;

   Typically they haven't used taylor series for a long time. They were replaced by Pade approximants and economized polynomials. These provide better accuracy over a wider range than a Taylor series.  A human thinks of  the number line as having all the real numbers but to a computer there are lots of missing numbers on it. Simply, because many numbers are not expressible in binary on a finite machine. Like 1/3,1/6,1/9... for instance.

bobbym

#56041 Re: Exercises » Challenge of the Day: » 2009-04-18 03:23:11

Hi ganesh;

My answer for #6

This is a bernoulli trial so:

#56042 Re: Puzzles and Games » Puzzlers - you can use the "Hide" tag » 2009-04-18 02:07:29

Hi quittyqat;

   The 3rd one looks best to me.

#56043 Re: Exercises » Prove composite » 2009-04-17 17:24:45

Sorry Jane, I was being nosy. Thanks for the invite. I already do a lot of lurking there.
(Hope you did not see the rest of this post before I got a chance to delete it. Stupidly, put my foot in my mouth with that thoughtless comment.)

#56044 Re: Dark Discussions at Cafe Infinity » Reaction of alkali metals with water » 2009-04-17 17:21:24

Hi Tigeree;

  I was being funny, it looks fine here too.

bobbym

#56045 Re: Exercises » Play with numbers » 2009-04-17 12:28:49

Hi smiyc86;

Here is my answer to #1, I hope it is what you require.

As you know the way to sum all the digits of any number is to take that number mod 9.
1999 is congruent to 1 mod 9 so 1999^1999 is also going to be congruent to 1 mod 9.
Therefore D = sum of the digits of 1999^1999 = 1

Also for fun:

B=29656
C=28

bobbym

#56046 Re: Exercises » Prove composite » 2009-04-17 08:55:12

Hi Jane;

  Thanks for providing the solution. Checking out the scienceforum link you provided their is a member that is like you but under another alias. On checking out her profile it leads to the invision forum where you appear as Jane Fairfax.

bobbym

#56047 Re: Exercises » find all positive integers to » 2009-04-17 00:25:06

Hi Tony123;

   What are you asking for? Are you asking for what value of n that would make that sum equal 400, because I don't think that is possible.

bobbym

#56048 Re: Exercises » few quants problems » 2009-04-16 23:53:43

Hi smiyc86;

Here is a quick and very ugly way to get the real roots of   (sinx)^4-(sinx)^5-(cosx)^5 = 2

First I notice that big 2 on the rhs and guess that one of the extrema of sin(x) and cos(x) are the answer. We have:






Just trying the first one yields (-1)^4 - (-1)^5 - 0 which equals 2 so x = -π/2 is one solution. Since sin is periodic


with c=0,1,2,3... are all solutions.

There are also complex solutions but I could not get them without resorting to an iterative method so I left them out.

bobbym

#56049 Re: Dark Discussions at Cafe Infinity » Reaction of alkali metals with water » 2009-04-16 21:54:48

Hi;

   It is apparent to me that Jane needs bigger smilies or I need bigger eyes, I totally missed that little guy.

bobbym

#56050 Re: Dark Discussions at Cafe Infinity » using calculators as proof » 2009-04-16 21:46:25

Hi Mikau;

   Your counterexample n=5 and x=5.1 should have convinced your teacher that you were right and that there is something wrong with his proof. Unfortunately, he is not wrong about calculators and even frontline computer algebra systems. In some cases they will experience loss of significant digits due to subtractive cancellation and or smearing.

bobbym

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