Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

Why is the Hole below a Lock?

You are given a set of weighing scales and 12 marbles. The scales are of the old balance variety. That is, a small dish hangs from each end of a rod that is balanced in the middle. The device enables you to conclude either that the contents of the dishes weigh the same or that the dish that falls lower has heavier contents than the other. The 12 marbles appear to be identical. 11 of them are identical, and one is of a different weight. Your task is to identify the unusual marble and discard it. You are allowed to use the scales three times if you wish, but no more. Note that the unusual marble may be heavier or lighter than the others. You are asked to both identify it and determine whether it is heavy or light

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

There were three women in all the swimming costumes!
One was happy and the other two were sad!
The happy one was crying and the sad ones were smiling.
Why was this?

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

which number am I?

Why do you find that most of the buildings are deprived of the 13th floor?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?