***** Extra problem for you ...... "Expand (x-y)3 " ...... solution at the exit. *****
Solutions of

***** Problem 1 *****

Count numbers of letters
"An odd number plus an odd number"...26 (even) letters
"An even number plus an odd number"...27 (odd) letters
"An even number plus an even number"...28 (even) letters
"An odd number times an odd number"...33 (odd) letters
"An odd number times an even number"...34 (even) letters
But: "An even number times an even number"...35 (odd) letters !!
And more, "even number" is even number and "odd number" is odd number.

***** Problem 2 ****** Thus, no triangle remained.

***** Problem 3 ***** 19.

2x4+1x3=11, 2x8+1x1=27, 3x3+1x7=16 ...... 3x5+2x2=19, 4x6+1x9=33,
5x2+3x3=19, 5x3+1x9=24

The solution you inspired at first, 13, was correct if the final number was 34, not 24.

***** Problem 4 *****

***** Problem 5 ***** 0 (zero).

Because the twenty-fifth member is (x-x). x-x is zero!

***** Problem 6 ***** 2000

Any way, spell down.

two, four, six, thirty, thirty two, thirty four, thirty six, forty ...... sixty six ......two thousands.

No numbers contain "e" !
I avoided "a thousand".
"one", "two", "three" system is more rational than "a", "two", "three" system.
I found this idea about 10 years ago, but I did not use this until Christmas card in 1999.

***** Problem 7 *****

***** Problem 8 *****

  1. From 9:59:59 to 10:00:01 ...... just 2 seconds
  2. From 1:33:31 to 13:33: 31 ...... just 12 hours
  3. From 15:55:51 to 20:00:02 ...... 4 hours, 4 minutes and 11 seconds

***** Problem 9 *****

***** Problem 10 *****

***** Problem 11 *****

***** From NOB ----- You know the following book *****

The Mathemagician and Pied Puzzler -- A Collection in Tribute to Martin Gardner --
from A.K Peters. ISBN : 1-56881-075-X

I sent "Creative Puzzle Thinking" with solutions to editor, but unfortunately, its solution part was lost in the book. I don't know why. Many people wanted its solutions. So I finished this. Enjoy them.
My newest mathemagic book sells well now in Japan, It contains 101 problems, not Dalmatians. I'm planning to publish its English version. When published, I will let you know through NOBNET (nobnet@iijnet.or.jp).

Happy Puzzling!
Bye from bad boy NOB.
***** Solution of the entrance: (x-y)3 *****