why number 8549176320 is one of a kind?

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

Can you count the number of triangles inside a triangle?

Prove that twice of ten is the same as twice of eleven.

Using Only Five 5's and any mathematical operator make sum as 37

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

What Time Should the last watch show in the below figure?

A frog is at the bottom of a 30-meter well. Each day he summons enough energy for one 3-meter leap up the well. Exhausted, he then hangs there for the rest of the day. At night, while he is asleep, he slips 2 meters backwards. How many days does it take him to escape from the well?