Last visit was: 18 May 2026, 13:10 It is currently 18 May 2026, 13:10
Home
Messages
Tests
Schools
Events
Close
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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 18 May 2026
Posts: 110,678
Own Kudos:
815,592
 [3]
Given Kudos: 106,295
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 110,678
Kudos: 815,592
 [3]
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 03:06
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

55% (hard)

Question Stats:

57% (01:46) correct 43% (02:07) wrong based on 114 sessions

History

Date
Time
Result
Not Attempted Yet
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5
ShowHide Answer
Official Answer
E
User avatar
Archit3110
User avatar
Major Poster
Joined: 18 Aug 2017
Last visit: 18 May 2026
Posts: 8,650
Own Kudos:
5,198
Given Kudos: 243
Status:You learn more from failure than from success.
Location: India
Concentration: Sustainability, Marketing
GMAT Focus 1: 545 Q79 V79 DI73
GMAT Focus 2: 645 Q83 V82 DI81
GPA: 4
WE:Marketing (Energy)
Products:
GMAT Club Tests
GMAT Focus 2: 645 Q83 V82 DI81
Posts: 8,650
Kudos: 5,198
A watch manufacturer has two factories (FA, FB) and 60% of their watch Updated on: 31 Jan 2019, 09:01
Originally posted by Archit3110 on 31 Jan 2019, 03:12.
Last edited by Archit3110 on 31 Jan 2019, 09:01, edited 1 time in total.
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5
Show more

total watches be 100
watch made at FA= 60 and FB= 40
defective watch FB= 40*.15= 6
so P defective watch FB = 6/100 = .06


Total defective watches A 6 & B 6 : 12

So question has asked a selected defective watch if selected would be of B
6/12 = 0.5 IMO E
User avatar
Mo2men
User avatar
Joined: 26 Mar 2013
Last visit: 09 May 2023
Posts: 2,426
Own Kudos:
1,510
Given Kudos: 641
Concentration: Operations, Strategy
Schools: Erasmus (II)
Products:
My Reviews
Schools: Erasmus (II)
Posts: 2,426
Kudos: 1,510
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 05:00
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5
Show more

Dear GMATGuruNY

Can you please share your thoughts on this question?

Thanks
User avatar
Archit3110
User avatar
Major Poster
Joined: 18 Aug 2017
Last visit: 18 May 2026
Posts: 8,650
Own Kudos:
5,198
Given Kudos: 243
Status:You learn more from failure than from success.
Location: India
Concentration: Sustainability, Marketing
GMAT Focus 1: 545 Q79 V79 DI73
GMAT Focus 2: 645 Q83 V82 DI81
GPA: 4
WE:Marketing (Energy)
Products:
GMAT Club Tests
GMAT Focus 2: 645 Q83 V82 DI81
Posts: 8,650
Kudos: 5,198
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 05:06
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Archit3110
Bunuel
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5
Show more

total watches be 100
watch made at FA= 60 and FB= 40
defective watch FB= 40*.15= 6
so P defective watch FB = 6/100 = .06


Total defective watches A 6 & B 6 : 12

So question has asked a selected defective watch if selected would be of B
6/12 = 0.5 IMO E

Posted from my mobile device
User avatar
GMATGuruNY
User avatar
Joined: 04 Aug 2010
Last visit: 17 May 2026
Posts: 1,347
Own Kudos:
3,919
Given Kudos: 9
Schools:Dartmouth College
Expert
Expert reply
Posts: 1,347
Kudos: 3,919
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 05:18
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5
Show more

Let the total number of watches = 100, implying that the number made at FA = 60% of 100 = 60 and that the number made at FB = 100-60 = 40.
Total number of defective watches = (10% of the 60 FA watches) + (15% of the 40 FB watches) = 6 + 6 = 12.
Since 1/2 of the defective watches are made at FB, the probability that a selected defective watch is made at FB = 0.5.

Show Spoiler
E
User avatar
Mo2men
User avatar
Joined: 26 Mar 2013
Last visit: 09 May 2023
Posts: 2,426
Own Kudos:
1,510
Given Kudos: 641
Concentration: Operations, Strategy
Schools: Erasmus (II)
Products:
My Reviews
Schools: Erasmus (II)
Posts: 2,426
Kudos: 1,510
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 05:27
Kudos
Add Kudos
Bookmarks
Bookmark this Post
GMATGuruNY
Bunuel
A watch manufacturer has two factories (FA, FB) and 60% of their watches are made at FA. It is known that 10% of them are made at FA and 15% made at FB are defective. What is the probability that a selected defective watch was manufactured at FB?

A. 0.05
B. 0.06
C. 0.066
D. 0.11
E. 0.5

Let the total number of watches = 100, implying that the number made at FA = 60% of 100 = 60 and that the number made at FB = 100-60 = 40.
Total number of defective watches = (10% of the 60 FA watches) + (15% of the 40 FB watches) = 6 + 6 = 12.
Since 1/2 of the defective watches are made at FB, the probability that a selected defective watch is made at FB = 0.5.

Show Spoiler
E
Show more

Thanks GMATGuruNY

But here is a question, why do not we make as follows:

Probability to pick a defective part of FA = 6/60

Probability to pick a defective part of FB = 6/40

Probability to pick a good part of FA = 54/60

Probability to pick a defective part of FB = 6/40

probability to select defective watch = (Probability to pick a defective part of FA)*(Probability to pick a defective part of FB)+(Probability to pick a good part of FA) * (Probability to pick a defective part of FB)

(6/60)(6/40) + (54/60)(6/40) = 6/40 =0.15

Where did I go wrong??

Thanks in advance
User avatar
EgmatQuantExpert
User avatar
e-GMAT Representative
Joined: 04 Jan 2015
Last visit: 02 Apr 2024
Posts: 3,651
Own Kudos:
21,008
Given Kudos: 165
Expert
Expert reply
Posts: 3,651
Kudos: 21,008
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 08:14
Kudos
Add Kudos
Bookmarks
Bookmark this Post

Solution


Given:
    • 60% of the watches are made at FA
    • 10% of the watches made at FA are effective, and
    • 15% of the watches made at FB are defective

To find:
    • The probability that the selected defective watch was manufactured at FB

Approach and Working:
Let the total number of watches be 100x
    • 60x are manufactured at FA,
      o 10% of 60x = 6x watches are defective

    • 40x are manufactured at FB
      o 15% of 40x = 6x watches are defective

    • Thus, total number of defective watches = 6x + 6x = 12x

Therefore, probability that selected defective watch was manufactured at FB = \(\frac{6x}{12x} = \frac{1}{2}\)

Hence, the correct answer is Option E.

Answer: E

User avatar
GMATGuruNY
User avatar
Joined: 04 Aug 2010
Last visit: 17 May 2026
Posts: 1,347
Own Kudos:
3,919
Given Kudos: 9
Schools:Dartmouth College
Expert
Expert reply
Posts: 1,347
Kudos: 3,919
A watch manufacturer has two factories (FA, FB) and 60% of their watch 31 Jan 2019, 09:00
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Mo2men
[Thanks GMATGuruNY

But here is a question, why do not we make as follows:

Probability to pick a defective part of FA = 6/60

Probability to pick a defective part of FB = 6/40

Probability to pick a good part of FA = 54/60

Probability to pick a defective part of FB = 6/40

probability to select defective watch = (Probability to pick a defective part of FA)*(Probability to pick a defective part of FB)+(Probability to pick a good part of FA) * (Probability to pick a defective part of FB)

(6/60)(6/40) + (54/60)(6/40) = 6/40 =0.15

Where did I go wrong??

Thanks in advance
Show more


P(selecting a defective part from FA) = P(selecting a part from FA) * P(the selected part from FA Is defective) = \(\frac{60}{100} * \frac{10}{100} = \frac{6}{100}\) = 0.06
P(selecting a defective part from FB) = P(selecting a part from FB) * P(the selected part from FB Is defective) = \(\frac{40}{100} * \frac{15}{100} = \frac{6}{100}\) = 0.06
Thus:
P(selecting a defective part) = 0.06 + 0.06 = 0.12

The value in blue represents ALL possible ways of selecting a defective part.
The value in green represents the GOOD ways of selecting a defective part (a defective part from FB).
Thus:
(good ways)/(all possible ways) =\(\frac{0.06}{0.12} = \frac{1}{2}\) = 0.5
Moderators:
Bunuel
Math Expert
110678 posts
Krunaal
Tuck School Moderator
852 posts