Replace the question mark with the number below given a simple math problem.

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

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

When we see 2 but call 10?

Two natural numbers have a sum of less than 100 and are greater than one.

John knows the product of the numbers and Jacob knows the sum of numbers.

The following conversation takes place between them:
John: 'I am not aware of those numbers.'
Jacob: 'I knew you wouldn't be. I am not aware myself.'
John: 'Now I know them!'
Jacob: 'Now I know them, too!'

What are the two numbers?

What shoe company does this rebus represent?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

In a school, there are four subjects. Seventy percent of students study English, seventy five percent of students study Science, eighty five percent of students study Mathematics and eighty percent of students study Spanish.

Can you calculate the percentage of students that study all four subjects?

In the given figure, you can see that four match sticks are used to form a square. Can you form five squares by using six matches?