# Coin Toss Model Probability

• May 12th 2010, 09:12 AM
boardguy67
Coin Toss Model Probability
Hi everybody!

So being a calc student and a stats student simultaneously is kinda fun, but i think its may be giving me tunnel vision. Argh!! Here's why...

If an alarm clock has a .5 probability of working, how many alarm clocks are required to reach a .99 probability that at least one will work?

So calc is blurring this thing for me, because i want to solve it with sum of series tools...which ain't workin'.

Sooo, what does work?
• May 12th 2010, 09:27 AM
shenanigans87
Quote:

Originally Posted by boardguy67
Hi everybody!
If an alarm clock has a .5 probability of working, how many alarm clocks are required to reach a .99 probability that at least one will work?

$.99=1-(.5^x)$

x = 6.64 alarm clocks... round up to 7.
• May 12th 2010, 09:32 AM
boardguy67
Sweet! Thanks Shenanigans! I suspected there was an easy way to do it that i wasn't seeing.