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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

5 coins are tossed. If two of them show heads, then the probability that all 5 coins show head is

a. 1/32 b. 1/10 c. 1/26 d. 1/13 e. none of the above

Total outcome:2^5=32
Outcome of at least two of them show heads:
Total-(1 head)-(0 head)=32-5-1=26
Outcome of 5 heads=1
Probability=1/26 _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Last edited by HongHu on 01 Apr 2005, 09:50, edited 1 time in total.

Sorry, the 1 is for 0 head, and the 5 is for 1 head. I'll edit the post to make it clearer.

Basically the question implies that two of them are heads but the other three can also be heads. So we need to know what probability is for getting at least two heads. It'll be total minus the cases where we only get one head, and where we get no heads. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

There are two explanations for this sentence "two of the coins show heads". One is that exactly two coins are heads. The other is at least two are heads. The next sentence askes "What probability is all coins show heads". You know that means in additional to the two heads, the other coins may show heads too. In other word there would be two or more heads, or at least two heads. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Sorry guys but I don't get this one. the question is :

5 coins are tossed. If two of them show heads, then the probability that all 5 coins show head is ?

We already know that 2 of them showed heads, no ? In my opnion it should be 1/8 becasue there are still 3 toss to make and the events are independant : (1/2)^3