What is the word or phrase?

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

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

What has 13 hearts but no other organs?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

What is the next number in this series?

4,12,84,3612....

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

A number can be multiplied by multiple of nine
i.e 9 18 27 36 45 ...

and the resulting number consist of only one digit.

Can you identify the number ?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

John and Jenni are a married couple. They have two kids, one of them is a girl. Assume safely that the probability of each gender is 1/2.
What is the probability that the other kid is also a girl?

Hint: It is not 1/2 as you would first think.