What goes up but never comes down?

If an electric train is travelling south, then which way is the smoke going?

A chicken farmer has figured out that a hen and a half can lay an egg and a half in a day and a half. How many hens does the farmer need to produce one dozen eggs in six days?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

Decode below rebus
D
N
A
T
S , D

Below is the sum of symbols in each row and column in the figure. Analyzing the figure, can you find out the value of the symbols?

O_er_t_o_

Complete the missing letters of the given word.

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 ?

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?

I’m tall when I’m young, and I’m short when I’m old. What am I?