Daily Challenges

[Sword]

Since we are all self-isolating, I wonder if members would like to post good puzzles, riddles, number games etc to help pass the time?

How about starting off with a chess puzzle? Not difficult but needs a bit of thinking. It was actually composed by one of the most famous chess players of all time.

Sorry, forgot to mention that it is White to move and mate in two.

 

Edited March 30, 2020 by Sword

[Unwilling Numismatist]

I looked at it for ages, I can't figure out whos go is next

 

[Sword]

Just now, Unwilling Numismatist said:

I looked at it for ages, I can't figure out whos go is next

 

Sorry, forgot to mention that it is White to move and mate in two.

[mrbadexample]

W: Ra5

B: pxa5

W: pb7

That works in my head but I'm crap at chess. 

[Sword]

Unfortunately pawns take diagonally and so you can't have pxa5. Even if pawns can take by moving forward after you W: pb7, it is still not mate because K can move to a7.

Really not a bad attempt for a non chess player.

[mrbadexample]

Black pawn takes rook at A5?

[mrbadexample]

Ahh...sorry, it's a6...looked like a 5 on the picture.

So replace a5 with a6.

[Paddy]

Yes, with the amendment that works. 1. Ra6, b7xa6, 2.b7 mate. (Black has no other legal move than b7xa6.)

 

[mrbadexample]

3 minutes ago, Paddy said:

Yes, with the amendment that works. 1. Ra6, b7xa6, 2.b7 mate. (Black has no other legal move than b7xa6.)

 

Black could move the bishop but then Ra7 = mate.

[Sword]

Correct. (And I don't believe you are bad at chess)

The alternative is R takes a7 check

B takes a7 is the only legal reply.

Pa7 mate

Edited March 30, 2020 by Sword

[Unwilling Numismatist]

Rook to A7 but I'm late back to the party - only 1 move required though.

[Diaconis]

With only two hourglasses, one of  7 minutes and one of 11 minutes you want to hard boil (very hard) an egg for exactly 15 minutes...

[Sword]

Turn both over. When the sand empties on the 7 mins hourglass, immediately turn it over again. Whe the 11 mins hour glass empties, the 7 mins hourglass now has 4 mins of sand. Turn that over to get the 4 mins needed.

[Unwilling Numismatist]

start both, flip the 7 min one when  empty, when 11 min is empty flip the 7 minute one to use the 4 minutes.. = 15 minuutes.

QED

[Sword]

24 minutes ago, Unwilling Numismatist said:

Rook to A7 but I'm late back to the party - only 1 move required though.

B will take a7 and so pawn b7 is needed as 2nd move to mate

[Unwilling Numismatist]

1 minute ago, Sword said:

B will take a7 and so pawn b7 is needed as 2nd move to mate

I resign from chess.

[mrbadexample]

3 hours ago, Sword said:

Correct. (And I don't believe you are bad at chess)

The alternative is R takes a7 check

B takes a7 is the only legal reply.

Pa7 mate

This doesn't work. Pa7 will be followed by Ka7. Pb7 doesn't work either because b7 is occupied. I think.  

I am terrible at chess. I know how the bits move and not much more, but I like a puzzle and there weren't many pieces involved. 

Edited March 31, 2020 by mrbadexample

[Sword]

9 hours ago, mrbadexample said:

This doesn't work. Pa7 will be followed by Ka7. Pb7 doesn't work either because b7 is occupied. I think.  

I am terrible at chess. I know how the bits move and not much more, but I like a puzzle and there weren't many pieces involved. 

You are right. I must have gone mad with cabin fever...

[Unwilling Numismatist]

You are in a room that has three switches and a closed door.

The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again.

How can you definitively tell which switch is connected to each of the light bulbs?

[Sword]

Turn on switch one for 5 mins. Then turn off and turn on switch two. Then open door. The bulb which is hot and off is controlled by switch 1. The bulb which is on is switch 2. The bulb which is off and cold is switch 3. 

Or you can just look through the gap at the bottom of the door or the key hole. 

[Diaconis]

One with a numismatic flavour. You can do this simply with a pen and a piece of paper.

You turn your back and ask someone to draw any number of coins in a row. Just circles, no need to ask him to replicate the effigy of George V, though that would be fun. Then he is to cover them with his hand or a piece of paper so that you are unable to see exactly how many coins there are. He is to leave only the first coin visible.

When you turn around you tell him that you will now write down the exact number of head/tail combinations of all of the coins he has drawn.

You do this and when he lifts his hand to reveal exactly how many coins he drew, your prediction is spot on.

[mrbadexample]

4 hours ago, Sword said:

You are right. I must have gone mad with cabin fever...

Ra7 was what I tried to do to start with but it didn't work. 

[Unwilling Numismatist]

56 minutes ago, Sword said:

Turn on switch one for 5 mins. Then turn off and turn on switch two. Then open door. The bulb which is hot and off is controlled by switch 1. The bulb which is on is switch 2. The bulb which is off and cold is switch 3. 

Or you can just look through the gap at the bottom of the door or the key hole. 

Or the nanny cam as it has now been invented

 

[Paddy]

This is a famous old one, but maybe some here haven't met it before:

You are locked in a room with just 2 doors out. One leads to safety, the other certain death. Also in the room are two robots - one can only tell the truth, and the other always lies, but you don't know which is which. They know which door leads to safety and you don't.

You are allowed just one question to one of the robots. What do you ask to ensure you know which is the safe door to open?

 

Edited March 31, 2020 by Paddy
Inserting the vital 2!

[secret santa]

Paddy, you left out the crucial 2 doors out.