If it took eight men ten hours to build a wall, how long would it take four men to build it?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

I am a five-letter word under you,
Remove the first letter and I am above you,
Remove the second as well and I am around you.

Who am I?

In the following picture, E is going to slide the object down and as per the terrain and the physics, the round object is going to travel all the way till the end. Now, can you analyze who all people will die when it happens?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Why is the Hole below a Lock?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

See the given image carefully. What you have to do is move the blue checkers in the position of the black checkers and vice versa. You are only allowed to move the checker to an adjacent empty space. Do it in the least possible moves.