Twenty frogs are sitting on a log floating on the surface of a river. Two of them decide to jump off into the water.

How many frogs are there on the log at this moment?

What breaks yet never falls, and what falls yet never breaks?

Give it food and it will live; give it water and it will die.

How many times can you subtract the number two from the number fifty?

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

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

They do not possess flesh or feathers or scales or bone
But still, they are blessed with fingers and thumbs of their own.

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

These types of puzzles are known as charades. What you have to do is find two words that are referred to in the first stanza and the second stanza and put them together to form the third word in the third stanza.

Just for example, if my first refers to 'off' and my second refers to 'ice', then my whole will be office.

My first is present - future's past -
A time in which your lot is cast.

My second is my first of space
Defining people's present place.

My whole describes a lack of site -
A place without length, breadth, or height.