What is the centre of gravity?

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?

What can you see in the middle of March and April that you can never see in any other month?

What do you get if you add 2 to 100 four times?

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.

What has many teeth, but cannot bite?

What kind of storm is always in a rush?

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

Rearrange the letters in "new door" to make one word.

What seven-letter word has hundreds of letters in it?