I am white when I am dirty, and black when I am clean. What am I?

I cannot talk, but I always reply when spoken to. What am I?

Which Number is the odd one out?

A) 7145
B) 2716
C) 5321
D) 4135

There was a strange boy who was born before his father. How can this be possible?

Find out a multi-digit number that if multiplied by the number 9 or any of its multiplications products (i.e. 18, 27, 36, 45,..) will result in the multiplication factor repeated (n) number of times.

What 8 letter word can have a letter taken away and it still makes a word. Take another letter away and it still makes a word. Keep on doing that until you have one letter left. What is the word?

I have teeth but i don't bite. Who Am I ?

What has no start, end, or centre?

At my favorite fruit stand,
an orange costs 18,
a pineapple costs 27,
and a grape costs 15.
Using the same logic, can you tell how much a mango costs?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?