Suppose there are a million habitable planets in our galaxy, that one in ten are habitable, that one in a thousand planets with life had at some point had an intelligent civilization, and that one in a hundred civilizations that has ever existed is in existence now. Given this, how many civilizations are in existence now?
A) 10
B) 1
C) 1000
D) 100

Question

Quizplus · Accepted Answer

Given there are a million habitable planets, and one in ten are habitable, this means there are 100,000 planets with life (1,000,000 / 10). Out of these, one in a thousand had an intelligent civilization, which results in 100 civilizations (100,000 / 1,000). Finally, one in a hundred of these civilizations is in existence now, leading to 1 civilization currently existing (100 / 100).

Suppose There Are a Million Habitable Planets in Our Galaxy