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:

A certain jewelry store sells customized rings in which [#permalink]

Show Tags

15 Oct 2004, 12:21

1

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct
0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A certain jewelry store sells customized rings in which
three gemstones selected by the customer are set in
a straight row along the band of the ring. If exactly
5 different types of gemstones are available, and if
at least two of the gemstones in any given ring must
be different, how many different rings are possible?

When I went to work the problem I kept trying to do

5 possibilities for 1st stone
5 possibilities for 2nd stone
4 possibilities for 3rd stone

or 5*5*4 = 100.

I can see that this is not quite right (for one reason need to divide out identical cases), however can someone please explain why this method is wrong and, if possible, what it's trying to calculate?

tyagel, It is more complicated this way. You didn't count all the options.

There are 2 options:
1) All different = 5*4*3 = 60
+
2) 2 Equal, 1 Different = 5C2 * 2 * 3C2 = 60.

60 + 60 = 120.

Let me explain the second one:
5C2 : Pick 2 stones out of 5 ,
2 : Choose 1 of those two colors again.
3C2 : Pick two places for the identical colors, order doesn't matter.