Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

What does this below rebus puzzle mean?

They are the five precious gems of an everyday sort and all can be found on a Tennis Court. Who are they?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

Identify Me

Hint1: I am a god
Hint 2: I am a planet
Hint 3: measurer of heat

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

What's a single-digit number with no value?

An evil man kidnapped someone and made them take one of two pills. One was harmless, but the other was poisonous. Whichever pill the victim took, the kidnapper took the other one. The victim took their pill with water and died. The kidnapper survived. How did the kidnapper get the harmless pill?

How high do you have to count before you use the letter “a” in the English spelling of the whole number?