Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?

Why do we preferably have round manhole covers and not square ones?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

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?

Arrange the numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 above and below the division line in a manner that the thus formed fractions equal to 1/3.

(You can use one number only once)

How can you drop a raw egg from a height onto a concrete floor without cracking it?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

Find out the number of circles in the given picture having Illusion

The Little ant seems to be always confused. Do you know why?