Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

How many triangles are there on the puzzle below?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

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 ()

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Can you solve below mathematical equation?

2^1234 - 2^1233

What does this mathematical rebus means ?