Amusing Math Puzzles – Get 430 Brain Teasers to Exercise Your Brain

I need a math trick/game for my math course……something that can be proven with a fairly simple proof…..Ive looked everywhere and most of teh stuff is logic problems…(which have ridiculously complex proofs…) it can be a card trick/dice/dominoes but again, not too in depth. This is for a college course but she said we can do even a kids math trick as long as its proven. Any suggestions/websites would be great….Ive done so much research already!!! arrrghhghh

How about this:

Pick any number (well, almost any. less than 2,222,209 & positive let's say.)
Add 14
Multiply by 9
Subtract 8
Add up all the digits
Add 5
Add up all the digits again
Subtract 6… You now have the number zero regardless of what number you picked first.

x
x+14
9x + 126
9x + 118
sum of digits of (9x + 118) ≡ 9x + 118 ≡ 1 (mod 9) *
1 + 5 = 6 (mod 9)
6 – 6 = 0

*You may be required to prove that the sum of the digits of a number mod 9 is the same as the number mod 9

powered by Yahoo Answers

Readers have also enjoyed these related posts:

1. What Is a Fun Math Game I Could Play With My High Schoolers? We Are Reviewing——–any Ideas?
2. What Site Can I Go to That Has Those Math Games?
3. Math Puzzles for Extra Credit in a College Algebra Class?
4. Anyone Know Any Fun Math Tricks?