Replace the question mark with the correct number in the below-given picture?

What occurs twice in a week, once in a year but never in a day?

What is the centre of gravity?

Our product and our sum always give the same answer. Who are we?

What is the largest number you can write with just 3 digits?

Identify the hidden meaning behind this picture?

A river should be crossed by a father, a mother and their two sons and two daughters.
There are some rules that should be followed while crossing the river. There can be only two people in the raft while crossing. The daughters cannot be with their father unless there is the presence of the mother. The sons cannot be with their mothers unless the father is present. Unless the guard is on the board, the criminals cannot be with any of the family members. Only the adults like the father, the guard, and the mother knows to use the raft.

How will they cross the river?

Using Only Five 5's and any mathematical operator make sum as 37

If Bihan is 10, Anirudha is 20, and Kim and Seal are both 5, but Rikold is 10, how much is Kenniger by the same trend?

There is a place where if I stand up straight, I will still be considered sideways.