Puzzle: 100-story building, identify the lowest floor for which a marble will break?

Question

You have a 100-story building and a couple of marbles. You must identify the lowest floor for which a marble will break if you drop it from this floor.

1. How fast can you find this floor if you are given an infinite supply of marbles?
2. What if you have only two marbles?

Answer 1

Use Binary Search:

first step- 100/2=50, try to drop from 50th floor. not 1 cases

1- it breaks 2- It did not

If it breaks then obviously the floor should be below 50 otherwise above 50

Then again repeat Binary Search...

so in this way number of operaions = log (base 2) n, where n=100