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

Find the Odd One Out?
84129
32418
47632
36119
67626
72927

Prove that the below maths equation is true.

8 + 8 = 91

Find the value of "?" in the ball picture Riddle below:

I can sizzle like bacon,
I am made with an egg,
I have plenty of backbone, but lack a good leg,
I peel layers like onions, but still remain whole,
I can be long, like a flagpole, yet fit in a hole.

There is something which is always coming but never arrives?

An equation has been laid down using a few matchsticks. However, as you can see, the equation is not correct. Can you correct the equation if you are allowed to add or remove 5 matchsticks?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Can you name three consecutive days without using the words Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday?