What does below rebus means ?

What does this simple rebus mean?

No matter how little or how much you use me, you change me every month. What am I?

What brings you down but never up?

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

One evening there was a murder in the home of a married couple, their son and daughter. One of these four people murdered one of the others. One of the members of the family witnessed the crime.

The other one helped the murderer.

These are the things we know for sure:

1. The witness and the one who helped the murderer were not of the same sex.

2. The oldest person and the witness were not of the same sex.

3. The youngest person and the victim were not of the same sex.

4. The one who helped the murderer was older than the victim.

5. The father was the oldest member of the family.

6. The murderer was not the youngest member of the family.

Who was the murderer?

A horse was tied to a rope 5 meters long and the horses food was 15 meters away from the horse. How did the horse reach the food?

You have four chains. Each chain has three links in it. Although it is difficult to cut the links, you wish to make a single loop with all 12 links. What is the fewest number of cuts you must make to accomplish this task?

In the image given, you can find several triangles. Can you count them all?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?