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

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

Can you find the thief by just looking at the picture below?

In particular commonwealth games, a female participant won silver and gold medals for a single event.

How can this be possible?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

If you’ve got me, you want to share me; if you share me, you haven’t kept me. What am I?

Buy me, smell me or deliver me, I do not change.

Who am I?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Two old friends, Jack and Jill, meet after a long time, and discussing as:

Jack: Hey, how are you, man?

Bill: Not bad, got married and I have three kids now.

Jack: That's awesome. How old are they?

Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.

Jack: Cool..But I still don't know.

Bill: My eldest kid just started taking piano lessons.

Jack: Oh, now I get it.

How old are Bill's kids?

Who is that with a neck and no head, two arms and no hands? What is it?