Question I'm interested in

Assuming you have 1024 possibilities, if you divide half of the possibilites at each step it takes 10 steps to finish.

What about if you remove 1/4 of the possibilites

1/8 of the possibilites etc

How much longer does it take mathematically?  What is the formula/principle behind this?

log(# possibilities) / log(1/(fraction probabilities removed each step))