What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

How high do you have to count before you use the letter “a” in the English spelling of the whole number?

A man always keeps a spare tyre in his car. To make full use of all the five tyres, he changes the tyres in a manner that for a distance of 1, 00,000 km, each of them runs the same distance.

Can you calculate the distance travelled by each tyre on that journey?

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

Find three whole, positive numbers that have the same answer when multiplied together as when added together.

I ask Joseph to pick any 5 cards out of a deck with no Jokers.

He can inspect then shuffle the deck before picking any five cards. He picks out 5 cards then hands them to me (Jack can't see any of this). I look at the cards and I pick 1 card out and give it back to Joseph. I then arrange the other four cards in a special way, and give those 4 cards all face down, and in a neat pile, to Jack.

Jack looks at the 4 cards i gave him, and says out loud which card Joseph is holding (suit and number). How?

The solution uses pure logic, not sleight of hand. All Jack needs to know is the order of the cards and what is on their face, nothing more.

There are forty elephants and they have forty-fore heads. How can this be possible?

Replace the question mark with the correct number.

Can you write down eight eights so that they add up to one thousand?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?