Why do people go to bed?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

What is harder to catch the faster you run?

If 21x = 79x, what is the value of x?

I don't get anymore wetter, no matter how much rain falls on me.

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

John was born on March 5, 1970, in Delhi, India. Jacob was born 25 days before John. The year when they took birth, Republic Day fell on Monday.

Can you find out on what day was Jacob born?

If 1+9+8=1, what is 2+8+9?

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

Why is the Hole below a Lock?