Can you convert the number zero(0) into a positive number using just one mathematical operator ?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

What happened when the wheel was invented?

As a whole I am both
safe and secure.

Behead me and I become
a place of meeting.

Behead me again and I am
the partner of ready.

Restore me, and I become
the domain of beasts.

What am I?

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

A bank customer had $100 in his account. He then made 6 withdrawals. He kept a record of these withdrawals, and the balance remaining in the account, as follows:

Withdrawals Balance left
$50 $50
$25 $25
$10 $15
$8 $7
$5 $2
$2 $0
----- -----
$100 $99

Why are the Totals not tallying?

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

What does does this rebus picture means ?

Solve the counting riddle by identifying the number of triangles in the given picture.