Person Who knocked Over Monitor!

What's the entire matter? 

If we assume Jessica speaking the truth & she is not the culprit then other 3 must be liar. The truth that comes from Nicole's statement is that Sandy is telling truth. But only 1 is speaking truth not 2 as here Sandy & Jessica.

That means Jessica is lying. Which in turn means it was she who done that damage. Now Sandy's statement can't be true as we already have got culprit Jessica. 

Similarly, Mellisa lying as she is pointing towards Sandy.Two person not telling truth at a time as per provided information.

So only left with Nicole who is telling the truth that Sandy is liar.

Hence we can conclude that, Jessica knocked over the monitor & Nicole is telling the truth.

Who is Liar?

Suppose there are twin brothers; one which always tells the truth and one which always lies.  What single yes/no question could you ask to either brother to figure out which one is which? (Condition is you can't ask question whose answer you already know. e.g. does earth rotate around the sun?)

This should be that question! 

Source 

Question To Identify Liar/Truth Teller

First know about twins. 

We should ask one question,

"Would your brother say that you tell the truth?"

Now if the question is asked the truth teller, then he knows his liar brother would say NO to this question. Hence he would say NO straightaway.

And if the question being asked to liar then he knows that his brother is going to say NO to this question but as a liar he would lie once again & would say YES to the question asked.

So depending on what reply we get, we can easily identify the liar & truth teller brother.

Remove Matches To Match Number

Remove six matches to make 10.

Shown here how it can be done!

  

Matches To Match Number

What was the challenge? 

It's pretty simple one. Nowhere it is mentioned that you have to make it as 

10 & not allowed to make TEN. So three sticks from first, one from second & 

2 from third gives us TEN.

However, we can make it as 10 as well. Removing 1 stick from first, 4 from 

second & 1 from third produces 10.

The True Statement?

A. The number of false statements here is one.

B. The number of false statements here is two.

C. The number of false statements here is three.

D. The number of false statements here is four.

Which of the above statements is true?

     Find it here! 

 Source

The Only True Statement

How it was tricky & what were others? 

One has to be true & other 3 must be false. Let's consider each case one by one.

Case A : According to this statement the number of false statement is 1 which is contrary to given condition that 1 is true & 3 are false. So it can't be true.

Case B : As per this, number of false statements = 2 which is again contrary to given condition of 3 false statements.So it can't be true.

Case C : As per this, number of false statements =3 exactly matching the given condition.

Case D : This implies number of false statements = 4 meaning that all the statements including itself are false. This is opposite to given condition. So this has to be false as well.

   
So the statement C is true & all other are false!