Math Puzzles (Read the Rules!)

[chiggins]

But you have only 2 Hourglasses, one measures 7-minutes, and the other measures 4-minutes. How can you correctly measure 9 minutes?

Start the 7 and 4 together, when the 4 runs out, the 7 will have 3 left.

Flip the four, when the 7 runs out, there'll be one left on the 4. Start the egg.

Once the four's done, flip twice for 8 more.

[Timko]

Flip 7 and 4
When 4 is out, flip again
When 7 is out, start boiling eggs
When 4 is out, flip again -> 1 minute
When 4 is out, flip again -> 5 minutes
When 4 is out, flip again -> 9 minutes
Eat said eggs

DAMNIT, beaten to the punch!

[NoLifeLeft]

Ahem.

1. The person who answered the last puzzle HAS to ask the next one. If you don't want to play, then don't reply.

BTW: you can save 7 minutes by...

0 min: Flip both & start eggs
4 min: 4 min hourglass finishes, flip it.
7 min: 7 min hourglass finishes, flip it.
8 min: 4 min hourglass finishes again, flip the 7 min hourglass that has only run 1 min.
9 min: 7 min hourglass finishes again, pull eggs.

[chiggins]

Ahem.

1. The person who answered the last puzzle HAS to ask the next one. If you don't want to play, then don't reply.

Workin' on it

[Timko]

Ahem.

1. The person who answered the last puzzle HAS to ask the next one. If you don't want to play, then don't reply.

BTW: you can save 7 minutes by...

0 min: Flip both & start eggs
4 min: 4 min hourglass finishes, flip it.
7 min: 7 min hourglass finishes, flip it.
8 min: 4 min hourglass finishes again, flip the 7 min hourglass that has only run 1 min.
9 min: 7 min hourglass finishes again, pull eggs.

That was the solution I was trying to think of. It's kinda funny that both me and Chiggins decided to solve the puzzle by not starting the eggs immediately.

[chiggins]

I like the old reliable, but I don't imagine this one's gonna take long.

You have ten coins: 9 are genuine and all weigh 10g, one is a fake but you don't know whether or not it's heavy or light.

You have a pan scale, and you've been allowed 3 weighings to determine the fake coin. (Wait, you ask, who's allowing me the weighings?) Oh, it's a um... it's a Sultan, very rich and powerful, wearing silk. Big huge beard. I'm reasonably sure that if you fail, his bare-chested, scimitar-wielding executioner will behead you for your mistake.

Find the fake!

[chiggins]

That was the solution I was trying to think of. It's kinda funny that both me and Chiggins decided to solve the puzzle by not starting the eggs immediately.

There's always something else to prepare or clean in the kitchen during the down time.

[J-Bolt]

Divide into four groups 3, 3, 3, and 1

Weigh the first two groups of 3.

If first weighing is equal, replace one group of 3 with the unused. If the new group is lighter, you know the odd coin is lighter, and you can pick 2 of the 3 and weigh. If unequal, pick the lighter one. If equal, last coin is lighter.

If the first weighing is unequal, keep the heavier group and replace the light group with the 3rd group of 3. If equal, measure out the removed group for the light coin. If unequal, measure out the heavy group for the heavier coin.

[Timko]

Oh crap. I was trying to solve this with 9 coins total.

[chiggins]

Ding!

A[1,2,3], B[4,5,6], C[7,8,9], D[10]

First weighing: A v. B

- Equal: know that the odd coin is in C or D
-- second weighing: C1 v. C2
--- Equal: odd coin in C3 or D, weigh any other coin against C3, equal means D is odd (I believe this is the only case where you don't know if the counterfeit is heavy or light)
--- Unequal: odd coin in C1 or C2, weigh either against any other coin to find odd coin

- Unequal: know that odd coin is in A or B. Refer to groups now as L(ight)/H(eavy)
-- second weighing: L v. C
--- Equal: odd coin is H and heavy, weigh two of three from H to find the heavy one
--- Unequal: odd coin is light and in L, weigh two of three from L to find the light one

Watcha got J-Bolt?

[Timko]

I wrote a problem at lunch (I learned it informally a long time ago, but I put some numbers with it), now I just need to answer one so I can give it to you.

[Leopard]

I wrote a problem at lunch (I learned it informally a long time ago, but I put some numbers with it), now I just need to answer one so I can give it to you.

how many midranges does it take to.. eh whatever


now proceed.

[chiggins]

Oh crap. I was trying to solve this with 9 coins total.

Dude, I found one with 12 coins in three weighings where the bonus super-hard restriction was, "non-adaptive". I do not have the math chops to figure out how he arrived at this answer, but check out the results table.

Now that's elegant.

[NoLifeLeft]

how many midranges does it take to.. eh whatever

None








bitches

[Timko]

I wrote a problem at lunch (I learned it informally a long time ago, but I put some numbers with it), now I just need to answer one so I can give it to you.

how many midranges does it take to.. eh whatever


now proceed.

Actually, my problem breaks rules #3 (no high level topics).