Eight of us go fourth, not back, to protect our king from an attack. What are we?

If a shopkeeper can only place the weights on one side of the common balance. For example, if he has weights 1 and 3 then he can measure 1, 3 and 4 only. Now the question is how many minimum weights and names of the weights you will need to measure all weights from 1 to 1000? This is a fairly simple problem and very easy to prove also.

What's the best place to go shopping in the ocean?

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

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

What you cannot hold but it is yours?

Solve this logical number series puzzle by replacing the question mark with the correct number
9090 = 4
1234 = 0
6055 = 2
9081 = 4
8888 = ?

What's the only room from which no one can enter or leave

In the picture given below, can you find out which digit will take place of the question mark?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?