Before Mount Everest was discovered, what was the highest mountain in the world?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

What is the below Rebus indicate?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

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

How can you take 2 from 5 and leave 4?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

What does below pictogram mean?

If your uncle’s sister is not your aunt, what relation is she to you?