What is the word or phrase?

In a mathematical quiz, you are asked the following question:

Use three 9s in a mathematical expression without dividing or multiplying to form the number one.

Can you answer the question?

Today, I celebrated my 32nd birthday but I was born in 1972.
How is this possible?

There is an exact a week gap between Christmas and New Year. Hence, It is obvious that the new year that comes right after Christmas comes on the same day of the week.

A Strange thing happened in the Year 1777. Christmas occurs on Wednesday and New Year on Monday. How is that possible?

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

A car is crossing a 20 km-long bridge. The bridge can support at most 1500kg of weight over it. If somehow, the weight on the bridge becomes more than that, it will break.

Now, the weight of the car is exactly 1500kg. At the midway, a bird comes and sits on the roof of the car. This bird weighs exactly 200 grams.
Can you tell if the bridge breaks at this point or not?

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

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

Solve the following series:
AZ, GT, MN, __, YB

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.