What word begins and ends with an E, but has only one letter?

Replace the question mark with the correct number in below Picture:

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Count the number of triangles in the below picture?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

What is the next number in this series?

4,12,84,3612....

John has played 50 ODI's and his average is 50. How many runs should he score in his 51st ODI, so that his average score jumps to 51?

In the figure that has been attached to this question, each digit represents a digit. The similar letters carry the same integer value. Can you expose the original digits?

A patient was diagnosed with some ailment. He was given five different tablets to take at night at an interval of 15 minutes.

How long will it take the patient to consume all the five tablets?

Queen Elizabeth organised a royal party.

To Avoid uninvited guest royal family set a password.
Jack (an uninvited person) plan to enter the party. He stand nearby the door.

First guest comes, the security person said 'twelve' and guest replied with six.
Second guest comes , the security person said 'six' and guest replied with 'three'.

Jack thought is enough and he walked to the entry point. The security person said 'eight' , Jack replied smilingly 'four'.
He was immediately thrown out of the party. why ?