What has many keys but can’t open a single lock?

When can we add 2 to 11 and get 1 as the correct answer?

If two's company, and three's a crowd, then whats four and five ?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?

There are two dice with empty faces in front of you and a marker. You can mark any number on each of the faces of the two dice, but you have to display all 31 days of the month using the two of them.

Which numbers will you mark on which dice so that you can easily depict all the dates of the month?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

You are given 2 eggs.
You have access to a 100-storey building.
Eggs can be very hard or very fragile means it may break if dropped from the first floor or may not even break if dropped from 100th floor, Both eggs are identical.
You need to figure out the highest floor of a 100-storey building an egg can be dropped without breaking.
Now the question is how many drops you need to make. You are allowed to break 2 eggs in the process

Can you count the number of triangles in the given picture?

How can you leave a room with two legs and return with six legs?

I’m tall when I’m young, and I’m short when I’m old. What am I?