Can you find the odd number in the following?

2716, 4135, 5321 and 7145

Two friends were stuck in a cottage. They had nothing to do and thus they started playing cards. Suddenly the power went off and Friend 1 inverted the position of 15 cards in the normal deck of 52 cards and shuffled it. Now he asked Friend 2 to divide the cards into two piles (need not be equal) with equal number of cards facing up. The room was quite dark and Friend 2 could not see the cards. He thinks for a while and then divides the cards in two piles.

On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

Count the squares in the matchstick puzzle below?

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

What can jump higher than a building?

How can you throw a ball as hard as you can and have it come back to you even if it doesn't hit anything there is nothing attached to it and no one else catches or throws it.

How many points are there on the globe where, by walking one mile south, then one mile east and then one mile north, you would reach the place where you started?

What is so fragile that saying its name breaks it?

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

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211