-2

if the odds of seeing at least one shooting star in an hour is 90% - what is the probability of seeing at least one shooting star in 20 minutes

tommy teek
  • 7
  • Could you perhaps add what you think the obvious answer would be and why you think it's wrong to the post? That would make this a much better question. – Milo Brandt Nov 04 '14 at 02:49

1 Answers1

0

Consider three consecutive $20$ minute periods. Let $A$ be the event we see at least one shooting star in the first $20$ minute period, $B$ the event we see at least one in the second period, and $C$ the event we see at least one in the third period.

It is reasonable to suppose that $A,B,C$ are independent and equally likely. Let $p$ be the probability of $A$. Then the probability of not seeing a shooting star in the one hour period is $(1-p)^3$.

We are told that the probability of not seeing a shooting star in one hour is $0.10$, Thus $(1-p)^3=0.10$, and therefore $$p=1-(0.10)^{1/3}.$$

André Nicolas
  • 507,029