Last visit was: 21 Apr 2026, 02:27 It is currently 21 Apr 2026, 02:27
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.
Close
Request Expert Reply
Confirm Cancel
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
810,345
 [8]
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
 [8]
1
Kudos
Add Kudos
7
Bookmarks
Bookmark this Post
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
Kudos
Add Kudos
Bookmarks
Bookmark this Post
avatar
riyazgilani
Joined: 14 May 2014
Last visit: 13 Jun 2016
Posts: 36
Own Kudos:
6
 [1]
Given Kudos: 39
GMAT 1: 700 Q44 V41
GPA: 3.11
Products:
GMAT 1: 700 Q44 V41
Posts: 36
Kudos: 6
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
Kudos
Add Kudos
Bookmarks
Bookmark this Post
riyazgilani
Bunuel
Official Solution:

How many subsets of \(\{a,b,c,d\}\) including both \(a\) and \(c\) (order of elements does not matter) are there?

A. 3
B. 4
C. 5
D. 6
E. 7

Here are the four subsets: \(\{a, c\}, \ \{a, b, c\}, \ \{a, c, d\}, \ \{a, b, c, d\}\).

Answer: B

hi, Bunuel,

can we count {a,b,c,d} as subset of {a,b,c,d}..?
____________________________
Yes.
User avatar
danjbon
Joined: 14 Oct 2015
Last visit: 25 Oct 2021
Posts: 11
Own Kudos:
42
 [1]
GMAT 1: 640 Q45 V33
GMAT 1: 640 Q45 V33
Posts: 11
Kudos: 42
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
riyazgilani
Bunuel
Official Solution:

How many subsets of \(\{a,b,c,d\}\) including both \(a\) and \(c\) (order of elements does not matter) are there?

A. 3
B. 4
C. 5
D. 6
E. 7

Here are the four subsets: \(\{a, c\}, \ \{a, b, c\}, \ \{a, c, d\}, \ \{a, b, c, d\}\).

Answer: B

hi, Bunuel,

can we count {a,b,c,d} as subset of {a,b,c,d}..?
____________________________
Yes.

That does not make sense. How can a "sub" set be the same as the set?? {a,b,c,d} is not a subset of {a,b,c,d}. Agree to disagree.
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
810,345
 [3]
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
 [3]
2
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
danjbon
Bunuel
riyazgilani


hi, Bunuel,

can we count {a,b,c,d} as subset of {a,b,c,d}..?
____________________________
Yes.

That does not make sense. How can a "sub" set be the same as the set?? {a,b,c,d} is not a subset of {a,b,c,d}. Agree to disagree.

Mathematically B is a subset of A if every member of B is a member of A. So, a set is a subset of itself.
avatar
cricketer
Joined: 15 Dec 2014
Last visit: 18 Sep 2020
Posts: 6
Own Kudos:
2
 [1]
Given Kudos: 155
Location: Canada
Concentration: Strategy, General Management
Schools: Rotman '18
GMAT 1: 610 Q44 V31
Schools: Rotman '18
GMAT 1: 610 Q44 V31
Posts: 6
Kudos: 2
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
Buenel,

I have a (naive) question. Why (D,A,C,B) is not a subset of (A,B,C,D) - when order of elements doesn't matter ?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
810,345
 [1]
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
cricketer
Buenel,

I have a (naive) question. Why (D,A,C,B) is not a subset of (A,B,C,D) - when order of elements doesn't matter ?

A set, by definition, is a collection of elements without any order. (While, a sequence, by definition, is an ordered list of terms.)
avatar
cricketer
Joined: 15 Dec 2014
Last visit: 18 Sep 2020
Posts: 6
Own Kudos:
Given Kudos: 155
Location: Canada
Concentration: Strategy, General Management
Schools: Rotman '18
GMAT 1: 610 Q44 V31
Schools: Rotman '18
GMAT 1: 610 Q44 V31
Posts: 6
Kudos: 2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
cricketer
Buenel,

I have a (naive) question. Why (D,A,C,B) is not a subset of (A,B,C,D) - when order of elements doesn't matter ?

A set, by definition, is a collection of elements without any order. (While, a sequence, by definition, is an ordered list of terms.)


Thanks a lot. Very helpful/useful concept.
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
User avatar
BottomJee
User avatar
Retired Moderator
Joined: 05 May 2019
Last visit: 09 Jun 2025
Posts: 994
Own Kudos:
Given Kudos: 1,009
Affiliations: GMAT Club
Location: India
GMAT Focus 1: 645 Q82 V81 DI82
GMAT 1: 430 Q31 V19
GMAT 2: 570 Q44 V25
GMAT 3: 660 Q48 V33
GPA: 3.26
WE:Engineering (Manufacturing)
Products:
GMAT Focus 1: 645 Q82 V81 DI82
GMAT 3: 660 Q48 V33
Posts: 994
Kudos: 1,456
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
SamarthSoni214
Joined: 08 Nov 2023
Last visit: 08 Jun 2024
Posts: 1
Given Kudos: 13
Posts: 1
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
­=11pt=12.0ptUse Combinatorics:
set of 2: 1 (a & c only);
set of 3: 2C1 = 2;
set of 4: 2C2 = 1
User avatar
OmerKor
Joined: 24 Jan 2024
Last visit: 20 Jan 2026
Posts: 129
Own Kudos:
Given Kudos: 150
Location: Israel
GMAT Focus 1: 675 Q85 V82 DI83
GMAT Focus 1: 675 Q85 V82 DI83
Posts: 129
Kudos: 152
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hi Bunuel,

Do you have a link to similar questions?
I want to work on this topic.
thanks :)
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
810,345
 [3]
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
 [3]
1
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
User avatar
OmerKor
Joined: 24 Jan 2024
Last visit: 20 Jan 2026
Posts: 129
Own Kudos:
152
 [1]
Given Kudos: 150
Location: Israel
GMAT Focus 1: 675 Q85 V82 DI83
GMAT Focus 1: 675 Q85 V82 DI83
Posts: 129
Kudos: 152
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Thank you.
you are the best.
Bunuel
User avatar
dueconcern4024
Joined: 23 Nov 2020
Last visit: 22 Oct 2025
Posts: 4
Given Kudos: 69
Posts: 4
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
As from the set {a,b,c,d} the subsets must­ contain {a,c} our task reduces to finding subsets of the remaining elements.

The set now - {b,d} has 2 elements. The total number of subsets for any set with n elements is given by 2^n. Therefore, the number of subsets of {b,d} is:
2^2 = 4­
User avatar
blablablashreya
Joined: 26 Apr 2023
Last visit: 15 Jan 2026
Posts: 2
Given Kudos: 5
Location: India
Posts: 2
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
why are we taking {a,b,c,d} as a subset?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 21 Apr 2026
Posts: 109,715
Own Kudos:
Given Kudos: 105,795
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,715
Kudos: 810,345
Kudos
Add Kudos
Bookmarks
Bookmark this Post
blablablashreya
why are we taking {a,b,c,d} as a subset?
Discover the answer to this question and other interesting points by reviewing the discussion.
Moderators:
Math Expert
109715 posts
Founder
43142 posts