My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum

LinkBack Thread Tools Display Modes
September 24th, 2009, 10:05 PM   #1
Joined: Sep 2009

Posts: 8
Thanks: 0

Simple probability problem...

...for some, but not for me.
If five coins are flipped simultaneously, what is the probability that at least two will be heads?
Could someone please post the formula for solving this particular problem?

Thanks and cheers,
Tyster is offline  
September 24th, 2009, 10:24 PM   #2
Senior Member
Joined: Oct 2007
From: Chicago

Posts: 1,701
Thanks: 3

Re: Simple probability problem...

You know the probability of each one landing heads is 1/2. (And tails is 1/2)
And when we want "x to happen" AND "y to happen" AND ..., we have to multiply the probabilities.
And finally, when we want "x to happen" OR "y to happen" OR..., we have to add the probabilites.

For exactly 2 heads, we need 3 tails. So, what is the probability of 2 heads, and 3 tails?

But we need *at least( 2 heads:

So, we can add: P(exactly 2 heads) + P(exactly 3 heads) + P(exactly 4 heads) + P(exactly 5 heads).

Or, we can realize that P(X happens) = 1-P(X doesn't happen),
and we can add: P(0 heads) + P(1 head), and subtract that from 1.

There's a slightly more advanced way of doing this (using combinations), but this is a simple enough problem that it's more trouble than it's worth.
cknapp is offline  
September 27th, 2009, 04:48 PM   #3
Joined: Sep 2009

Posts: 8
Thanks: 0

Re: Simple probability problem...

Thanks for the explanation. Cheers.
Tyster is offline  

  My Math Forum > High School Math Forum > Algebra

probability, problem, simple

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
simple probability Q lun123 Advanced Statistics 1 October 6th, 2013 05:21 PM
simple probability maxgeo Probability and Statistics 1 April 23rd, 2013 09:37 AM
Simple probability problem - please help! :) drwmn Probability and Statistics 1 October 10th, 2011 10:03 AM
simple probability forcesofodin Advanced Statistics 2 April 8th, 2010 11:36 AM
Probability problem (intuitively simple) johnny Algebra 4 August 2nd, 2009 03:33 AM

Copyright © 2019 My Math Forum. All rights reserved.