What occurs twice in a week, once in a year but never in a day?

The chance of Mr John winning the lottery is 10%. All participants lined up and Mr John is 4th in the row. The first three participants lose the lottery.

What is the chance of Mr John now?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

When is the top of a mountain similar to a savings account?

Through your logical capabilities, can you make 7 an even?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?

How can a man go eight days without sleep?

A boy purchased a book from a bookkeeper and gave him $100.
The cost of the book is $50 but the bookkeeper has no change, so he gets the change from the next shop and returns the boy his $50.

After some time the next shopkeeper came with the $100 note and told the bookkeeper that the note was a fraud, so he took the money back.

How much loss did the bookkeeper face?

There is a box. The area of its top is 240 square units, the area of the front is 300 square units and the area of the end is 180 square units.

Can you calculate the dimensions of this box with the given data?

Can you count the number of triangles in the picture below?