My Math Forum  

Go Back   My Math Forum > High School Math Forum > Probability and Statistics

Probability and Statistics Basic Probability and Statistics Math Forum


Reply
 
LinkBack Thread Tools Display Modes
August 24th, 2017, 10:36 AM   #1
Newbie
 
Joined: Aug 2017
From: Texas

Posts: 1
Thanks: 0

Beginner/Basic - Probability - Guessing Incorrectly

All,

First, I am not a statistics guy or really a math guy.

My question is a result of the recent PowerBall - "What are the odds of not drawing any correct balls?"

I know that the odds of winning are:
(5/69)*(4/68 )*(3/67)*(2/66)*(1/65)*(1/26)

I worked the logic for that by playing with a 2 digit number out of 00-99:
(2/10)*(1/10)= 20%

That makes sense the possible correct numbers are 12 or 21, etc

On my 2 digit example, the odds of getting no numbers correct is 80% (just by logic - I hope). However, the "math" I came up with is wrong:
(8/10)*(9/10) = 72%

I guess somehow the denominator of the 2nd term should be 9, yielding:
(8/10)*(9/9) and the 80% that makes sense. But I can;t understand why that denominator would be 9.

I think if I understood what I was doing wrong on the simple example, I could then develop the answer to - what are the odds of drawing no correct balls in the PowerBall

Thanks in advance.
mattstoc is offline  
 
August 24th, 2017, 10:58 AM   #2
Senior Member
 
romsek's Avatar
 
Joined: Sep 2015
From: Southern California, USA

Posts: 1,413
Thanks: 717

on the first white ball you have 64 possible balls that don't match any of the winning balls.

and similarly for the rest of the white ball draws.

there are 25 possible non-matching red balls.

so

$p = \dfrac{64}{69}\dfrac{63}{68}\dfrac{62}{67}\dfrac{6 1}{66}\dfrac{60}{65}\dfrac{25}{26} = \dfrac{31768800}{48700223} \approx 0.65$
romsek is offline  
Reply

  My Math Forum > High School Math Forum > Probability and Statistics

Tags
beginner or basic, guessing, incorrectly, probability



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Basic Probability Sashank Probability and Statistics 2 June 9th, 2016 07:36 AM
Probability of *not* guessing the right card in a 52-card deck... cbenson4 Probability and Statistics 1 March 5th, 2015 11:56 AM
Basic probability xsgx Probability and Statistics 5 October 21st, 2013 09:31 PM
Probability of guessing playing cards. adam678 Probability and Statistics 14 February 14th, 2013 12:57 PM
Basic Probability help downthesun01 Algebra 1 October 7th, 2009 02:49 AM





Copyright © 2017 My Math Forum. All rights reserved.