It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

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?

What do you call a fish without an eye?

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

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

When we see 2 but call 10?

There is a wide field of corn. A goose finds its way into the field and starts running. Can you find out till which point the goose can run into the field?

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

A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?