Name a key which is hardest to turn.

Find the next number in the series

12, 20, 40, 72, 116, 172 ?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

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 ?

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

A rain drop fell from one leaf to another leaf and lost 1/4th of its volume. It then fell to another leaf and lost 1/5th of the volume. It again fell on another leaf and lost 1/5th of the volume.



This process kept repeating till it fell on the last leaf losing 1/75th of its volume.



Can you calculate the total percentage of loss from the initial volume when the drop has fallen to the last leaf accurate up to two decimal places?

Identify the hidden meaning behind this picture?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

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