A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

When can we add 2 to 11 and get 1 as the correct answer?

I drive at an average speed of 30 miles per hour to the railroad station each morning and catch my train. On a particular morning, there was a lot of traffic and at the halfway point, I had averaged only 15 miles per hour. How fast must I drive for the rest of the way to catch my train?

How far can you walk into the woods?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

Can you find out the remainder when 3^300 is divided by 5?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

One day, John and his friends were playing around. Jacob hit something with a Pin and it popped. John's dad came into the room that very moment, but he wasn't mad. In fact, he was smiling. What did Jacob hit?

In the city of Brain Teasers, 5% of people do not list their phone numbers. Now if we select random 100 people from the phone directory, then how many people selected will have unlisted phone numbers?

Can you find a seven digit number which describes itself. The first digit is the number of zeros in the number. The second digit is the number of ones in the number, etc. For example, in the number 21200, there are 2 zeros, 1 one, 2 twos, 0 threes and 0 fours.