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

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

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?

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.

Arrange the numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 above and below the division line in a manner that the thus formed fractions equal to 1/3.

(You can use one number only once)

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?

Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

Find the number of squares in the below-given picture.

Our product and our sum always give the same answer. Who are we?