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

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

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

which number am I?

You need to arrange three 7 and mathematical symbols to form number 1?

In a classic wine shop, the list of three most popular wines are:
- The cost of 1 French wine bottle: 500$
- The cost of 1 German wine bottle: 100$
- The cost of 20 Dutch wine bottles: 100$

John entered the wine shop and he needs to buy
- All three types of wine bottles.
- Needs to buy Dutch wine bottles in multiples of 20.
- Need to buy 100 wine bottles in total.

John has only 10000$. How many wine bottles of each type, John must buy?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

How many triangles are there on the puzzle below?

Using four sevens (7) and a one (1) create the number 100. Except for the five numerals, you can use the usual mathematical operations (+, -, x, :), root and brackets ()

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?

Divide 110 into two parts so that one will be 150 per cent of the other. What are the 2 numbers?