Count the squares in the matchstick puzzle below?

The centre of the third figure is empty. What digit should fit inside?

Count the number of squares in the picture below.

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

What makes this number unique: 8,549,176,320?

Forwards I am heavy, backward I am not. What am I?

In The 1st month of this year(the year 2013), I noticed that the date 13-1-13 (13 January 2013) is special.

This date is special as:

Date * Month = Year.

Can you figure out which year of this century has a maximum number of such dates?

I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

I am lying and I always lie. Tell me whether I am lying or telling the truth.

Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= 48
5 + 5= ?