Count the number of triangles in the below picture?

What happened when the wheel was invented?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

During which month do people sleep the least?

In a football game, Christina defeated Teresa by 2 - 0 but no man from either side scored. How can this be possible?

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?

Find three whole, positive numbers that have the same answer when multiplied together as when added together.

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?