It is currently 18 Nov 2017, 16:51

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Probability Die

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Senior Manager
Joined: 05 Oct 2008
Posts: 267

Kudos [?]: 548 [0], given: 22

Probability Die [#permalink]

Show Tags

07 Jun 2010, 00:10
If a fair coin marked 1 and 2, and a fair die are rolled together, what is a probability to have the sum even?

(C) 2008 GMAT Club - m05#34

* $$\frac{1}{8}$$
* $$\frac{1}{4}$$
* $$\frac{1}{2}$$
* $$\frac{3}{4}$$
* $$\frac{7}{8}$$

The coin has 1 and 2, and the die has 1, 2, 3, 4, 5, 6 for a total of 12 possible outcomes. (aren't the total number of outcomes - 6*6 = 36?)

To get the final result even, we must have two even numbers, $$E$$ , or two odd numbers, $$O$$ .

$$E + E$$ is possible if we have $$2+2$$ , $$2+4$$ , $$2+6$$ .
what about 4+2, 4+4, 4+6, 6+2, 6+4, 6+6, ?? These total to even numbers as well?

$$O + O$$ is possible if we have $$1+1$$ , $$1+3$$ , $$1+5$$ , so there are six favorable outcomes out of 12 possible. $$\frac{6}{12}=\frac{1}{2}$$ .

Likewise, what about 3+1, 3+3, 3+5, 5+1, 5+3, 5+5??

This explanation does not take all the outcomes into consideration. Can someone explain how to get to the correct answer.

Thanks.

The correct answer is C.

Kudos [?]: 548 [0], given: 22

Manager
Joined: 20 Apr 2010
Posts: 151

Kudos [?]: 19 [0], given: 16

Location: I N D I A
Re: Probability Die [#permalink]

Show Tags

07 Jun 2010, 01:16
We can get the Sum Even in 2 cases which are : E + E or O + O

Probability of getting both Even : P( of getting 2 on coin ) * P ( of getting Even on die i.e. 2,4,6 out of total 6 possibilities and not 36 )
= 1/2 * 1/2 = 1/4

Probability of getting both ODD : P( of getting 1 on coin ) * P ( of getting Odd i.e 1,3,5 on die )
= 1/2 * 1/2 = 1/4

Total prob = 1/4 + 1/4 = 1/2

Hope its clear...

Kudos [?]: 19 [0], given: 16

Manager
Joined: 20 Apr 2010
Posts: 151

Kudos [?]: 19 [0], given: 16

Location: I N D I A
Re: Probability Die [#permalink]

Show Tags

07 Jun 2010, 01:21
E + E is possible if we have 2+2 , 2+4 , 2+6 .
what about 4+2, 4+4, 4+6, 6+2, 6+4, 6+6, ?? These total to even numbers as well?

The values highlighted r never possible as u r having one coin which can yield a value of 1 or 2 only....

Kudos [?]: 19 [0], given: 16

Re: Probability Die   [#permalink] 07 Jun 2010, 01:21
Display posts from previous: Sort by

Probability Die

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

Moderator: Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.